As for the universal praise, I do agree with a few that have said that many are being "told" to say "ohh and ahh" and that's not their genuine opinion, just following the crowd. Kind of like the people who played Ico late, after it got that "underground" praise years before, right? Alright, seriously though, moving on...
I do echo what someone else said that the "launch day" people may have had it the best. By when I say "launch day" I mean the week before the 'real' launch, when PS+ members got it.
The reasoning is simple...I'd reckon 80%+ of the people you'd meet (if you were playing within the first few hours it went up on US PSN) were going through their first time. I saw this very clear that it was also my companions' first time going through by the way they were exploring, some even standing still for a second or two to take in the new views.
A few days later when I was going for trophies, it was apparent a lot of people were going for trophies or already saw these areas before and were rushing through or the rare "know it all " types who were going for all the secrets and thus kind of spoiled their secret locations for you (well, not me, but the later people). The biggest issue may have been people quitting out mid-level. I did this only a few times because I was going for some trophies, and I felt bad for the wanderers that obviously seemed like it was their first playthrough.
At times I felt the "lone wanderer" approach could have been more effective than the "companion" approach, especially for example when looking for all the desert "creatures" to free in for the "Explore" trophy. I had to just disconnect from PSN because other people were rushing through the stage or 'saving' the creatures that I didn't find and explore around yet, fearing it'd negate the trophy. It was a nice touch at least that the devs disabled the "multiplayer" in the very first area/stage (as far as I know, because I never found anyone there).
Overall my first playthrough was good I thought. I really took my time on the first "stage". Upon looking in the distance in the second stage (the "broken bridge"), I saw what looked like a red cloth flowing across the sand, on top of it. I thought it was some kind of NPC or rare "sighting". Note I had completely forgotten about the "anonymous multiplayer" by the point of the game's release. So, I ventured over there and minutes later I found that it was actually another wanderer of the desert, just as I was.
I journeyed with this wanderer and we completed the next few areas/stages together. But...he disintegrated around mid-way through at the beginning of one of the stages (he quit out). I view this as a metaphor of life. That it is a long and grueling journey as is wandering this tough desert with little idea of where to go at times, the people that come along this journey, the people you shared special times with in the past, sometimes disappear and perish without warning. That you need to keep your head up despite these losses and succeed in this journey.
So, this can make you feel better if your first playthrough wasn't with the "same" person from start (well, second stage is where the earliest people can join I believe) to finish. With a companion to the end or people abandoning the journey, both have meaning when you take my idea on it into place. You, the wanderer, conquered the grueling journey while others perished. You can kind of see them as the gravestones. In fact, an added touch to the game would be that when someone quits out, instead of just disintegrating, they would leave behind one of the many gravestones (perhaps with a scarf attached like you see notably on the first "stage") you see in the game. It would echo the feel that you are the "lone" wanderer in a world covered in sand and perished souls who didn't reach the goal you are also trying to reach.
I finished my first playthrough as a "lone wanderer" and felt it may have had more significance that way, if it was "forced", but that's taking my "theory" (all wanderers perishing except one) into place, not the developer's intention - however I think this game is flexible enough that it allows many interpretations, as the devs more than likely intended.
My second playthrough was unique from my first. I was looking to get the "majority of journey together" trophy and waited around in stage 2 for a partner. A white and gold robed wanderer arrived, almost sage-like. I had not seen this before, I thought it could have been a developer or something, since he knew where every secret in the game was at pinpoint precision - although he did get his scarf snapped underground. He showed me where many secrets were, pretty much everything in the game - a good few I had no idea about. He waited up for me when I was behind, I waited for him. We worked together.
A memorable part was the final summit area where the screen is so bright you could hardly see. I lost track of where he was and thought that he turned his console off or got disconnected. I searched around the area and waited around (by the way, there totally should have been a collectible/orb/easter egg inside the mountain volcano/crater thing full of water that you can sink into), perhaps he got stuck at an earlier platforming part. I waited and waited and looked for about 10-15 minutes. I didn't want to get screwed out of the trophy after doing the entire playthrough with a companion. I figured he was gone. When I passed by the final part of the area (when you're going up that "wind tunnel" then arrive in a new area), there he was. Facing my direction, standing there. Waiting for me.
Later on I found that the white/gold robe was the prize for getting all the "orbs", but it was a special time journeying with this unknown entity.
Now, for the story. I'm not sure if there's an official word on it, or if the developers want other people to interpret it differently. My take on it is that this takes place in a time in the near distant future from modern times. A judgment day came (2012) and the wrath of the "gods" covered the entire world in sand. All oceans were dried and covered in this sand, all animal life was dead. Everything was sand. The entire globe is a desert.
A small village of people (most likely around India from the robes being worn) were selected to be the only ones left surviving. They were told that their main purpose was to re-create the world anew, since the old world was full of evil and corruption and their way of purging this was to cover the world in sand. The evil "flying searchlight worms" were placed on earth to keep the surviving humans on their toes, in ambition to reach the summit, purging these lurking evils and re-make life. If they failed to reach the summit, they would continue to live in this world of purgatory (purgatory meaning that they could continue to reproduce but their numbers would always be around the same due to journeyers going off and dying to the god's trials), until one lone villager finally passed the gods' trials and reached the summit, awarded the second coming of human civilization and life itself on earth.
The lone wanderer who is the one to reach the summit becomes the light (as you see in the game), ascending to the heavens, becoming a god, and is awarded by the other gods a place in the ethereal realm, now tasked with watching over the second coming of earth's civilization.
If you believe in the chance of "ancient astronauts" and theories, the above take on the story can get even more interesting. Which is why I put "gods" in quotes, you can think of it either way. For example, according to these theories, the first humans were made by them millions and millions and millions of years ago so the planet sees life besides animals and plants; perhaps a purpose of creating humans was to 'mine' some kind of essence or materials. Millions of years pass and the evils, sins and corruption of humans reaches an all-time high (2012). This negativity and manipulation/abuse of the earth's natural resources/atmosphere/etc cause the "essence" or materials the ancient astronauts are harvesting to deplete and be no more. So, this causes these "ancient astronauts" to douse the earth in sand, ending all living life except for one lone village. They are given the chance to start life and civilization on earth again, by overcoming trials and reaching the summit. Once that happens and the second coming of humans progress, the "ancient astronauts" can once again harvest whatever essence or material that is created with positive human life.
The "gods" take is much more simple than this alternate interpretation, though. Perhaps think of the "gods" take as Ending A (Good End) and "ancient astronauts" as Ending B (Evil End).
A being "good" because it's a re-birth of life on earth starting from square one with no negativity; B being "bad" because it's a re-birth but a cycle, a continuous manipulation of the human race for an outside race's personal gain.
As for wants for DLC...no, I don't want any on this one and feel the experience is complete. With flOwer (that's the official way to write it, right?), I felt that a lot of the game was kind of "on-rails" in that you could only explore sectioned off areas, always with an arbitrary goal (don't get me wrong, these were masterpiece decisions for the flow of the game and experience as a whole, just read on), and the things demonstrated such as changing colors and different petals could be expanded on. My idea was for a small post-"story" DLC that took place outside the "window" at the end, in the new world you brought color and light to. It would be a gigantic flower field, with each color/flower type. You could essentially "free roam" this, your actions changing the landscape - it would be a free area with no end goal, because the end goal of the game was already reached. Think of it was the flower petal "rejoicing" in this new euphoric world. I recall someone told my idea to Jenova Chen and the idea was shot down because he thought the experience was complete as is. Perhaps instead of this being a selectable level, it could have been the "credits" - you could select it later by interacting with the window. Of course, that'd take significance away from the credits sequence, but maybe it could have been added in afterward. It's not a huge deal, just an interesting idea. I'm sure if the devs saw this idea more clearly (or if I was part of the team) it could have worked alongside the other's visions. Even if not, I respect Jenova and co's vision and end product.