First, the story missions have zero variety. Deploy ghost, waves of enemies, progress further, sudden no respawn zone where more enemies are deployed and then a boss. The issue there is also one with the way the world is designed. The shared open part, to work with both 20+ and 5 makes it so across the board there is nothing but fodder spawning on 98% of the area, and it makes it so each mission has to funnel you into tunnels so they can instance you out of the game and plop down higher level enemies. As a shooter, this gets very grating as encounter design is the key to keep things fresh and when you can predict how everything is going to happen, it gets boring. Beyond this is the completely incomprehensible plot itself, the only thing that sheds any light on stuff is accessed via an app, and all of the characters are just giving you no reason to care about them. The vendors in the tower could be made an actual vending machine and lose nothing in the translation, as they never have an introduction or any real interaction beyond saying a one line quip randomly when you view their store. Unlike other shooters, Destiny doesn't capitalize on tight well designed encounters, nor does it craft a story worth a shit.
Then there's the loot. The majority of the weapons are very similar looking, and the brunt of everything interesting is all in the endgame which leaves the 1-20 climb not very interesting. You can rock it 5 games in a row in PvP and only get one single weapon the entire time that ends up being worse. You can run through the same strikes and get similar results, and nothing but green drops from the enemies which are totally useless once Light comes into play. The endgame focus becomes focusing on reputation and marks to afford loot and purchase it yourself, which is counterintuitive to the point of a loot game. The game frequently will give engrams to decode, but these can all jump down in value. A legendary engram can become a rare weapon, which keeps happening to me. It can also become an item for ANY OTHER CLASS, which literally never happened with commons, uncommons, and rares. They just make it even less likely to get a legendary you can even use, when it is already so incredibly rare to have one drop. It's possible you decode these and they just become actual items/special currency...this, again, is why everything is just focused on buying it all yourself. Unlike other loot games, Destiny doesn't integrate it well enough to feel like it's a satisfying chunk of the game. There's so much frustration involved, and the guns are all still grounded so you won't be seeing things like cows being summoned to fight for you, or a gun that as you reload you throw it and it levitates towards enemies shooting them until it blows up. Instead it gives you the same armor pieces twenty times each.
Next up, Patrols. I could use their video where they threw a grenade far into the distance then turned around because they had no time, but these issues stand out just by playing and don't even need that on top of it. You can go wherever you want, so get to exploring! First off, you probably want to find chests. And sure, there's a decent amount of them, all hidden away...but they tend to have barely anything. Here's some glimmer and whatever resouce the planet has on it. Also more uncommon gear, since that's just fantastic. Next, is actually finding these. They are at times pretty well hidden, which is actually clashing with how these landscapes are designed. The game is full to the fuckin' brim with these little caves that are clear spawn closets. They all look the same, are a single room with a rock jutting out, they're all over the place. Sometimes like on the moon they even have these little buildings that you can go in and look oddly similar, a single dead end room....because they're the same. These tend to have nothing in it, but CAN hold chests. This means the game encourages you to check these little spawn closets even if they're all copy and pasted, because some of them will hold shit. Why would you encourage players to do that? Otherwise, there's exploring with your guardian's abilities. All three classes can get very high with their jump, but the level design does not let you do much.
Here's an example. This is on top of a building on the moon, where a piece is broken off and serves as a bridge over to this hill. Can you tell me where the player can go, and where he can't? That lower part the bridge goes directly towards works, but just a little bit to the right with all the circles is a giant invisible wall that pushes you off. But sometimes you can get to areas like this totally fine, AND sometimes they have loot...so there is no consistent ingame logic about boundaries which is incredibly frustrating and immersion shattering. To add some more hilarity, there was once a chest I found at this spot on the other side of that hill, right by the invisible wall. After opening it, I stepped forward a bit to look out into the distance and found out that the back half of this has zero collision so you fall right through the moon to your death.
Here's another. Looks like a decent place to possibly put a chest or matierial, yeah? until you take a step down here and get a TURN BACK countdown warning that kills you. This entire spot in front of me is a giant killzone...but you can get to the spot behind it, and to the left of it. You circle around this whole spot, but the circle itself is death for...some reason. Again, this clashes with what a player would expect to be consistent ingame logic, and instead becomes guesswork on "can I actually go here, or will I die/smack into a wall?" and that is damning critique to an 'open world' game.
Moving on, Strikes! Fight through enemies, hit a big boss at the end. Sounds like fun, yeah? Most of the bosses are not well designed for this type of game. They are designed incredibly samey, having ranged attacks with an AoE splash, and a shockwave attack if you get close (gg to Titans who have a totally useless skillset as CQC is impossible and their super is suicide unless they're the subclass). On top of THAT, they have absurd amounts of HP for you to grind through as they keep walking around, shifting focus around players as you keep hitting them slowly but surely. Very few function like the spider tank which has a weakness to exploit to the point where it topples and opens up for a lot of damage. Though even this guy just sits idly by as everyone rains fire upon him instead of leaping around the massive space to fight him, which would have been a much more organic and hectic fight. To counterbalance, Bungie just takes a super easy way out and keeps spawning in enemy fodder to both pressure you from the sides and possibly distract you from the boss who will blindside you. But, mainly, you just save you super for them and get ammo back because you're running out pelting this sponge. The endgame content, apparently, is meant to be using a strike playlist to keep doing these at higher level, but ultimately these problems are hardly fixed at other difficulty levels. And then after you finally beat these, the game has the same issues with loot distribution where it's likely to give jack and shit all to actually progress you forward. And there's 6 of them total. And there's no way to vote on a map, so it keeps sending you to the same couple.
So as you can imagine, all of these pieces and parts intertwine and hold eachother back. The patrol worlds themselves seem barely designed around the actual jump capabilities of your guardian, and are trying to link up with people so the surface is full of fodder and generally uninteresting fights, so the game funnels you down into tunnels but still manages to just toss uninteresting boss fights at you which focus far too much on enemies that you know within the first few minutes you can already beat as you go through the motions again. Then the loot based part makes it so you're grinding this all to just buy the better weapons, which feels like an empty loop as the actual content being grinding has so many issues already.
The other part is PvP, which has its own slew of issues. Again, no map vote, so expect to see the same ones. Though special mention here as Bungie has always been so forward focuses with these types of things, how the hell did they go so far backwards on basic functionality? Weapon balance is still off from the beta though it's likely they're tweaking the hell out of this, but ARs and shotguns are overwhelmingly powerful, and each class can just pull nonsense out of their hat on a whim. Turn a corner into a guy with a golden gun, instant death. See a team capping a point as a titan drop a shield...I dunno, you got outplayed. Warlock and Titan yolo bombs, titans in particular starting up in an instant and having a hitbox the size of a nuke so you instantly die even if you see it coming and get away. You can fight it at some points, but on many others it's just a no win scenario based on a 2 second split decision as there's not enough notification that a player has a super ready. Grenades with AoE damage all over the place, and no way to track who tossed it. Did an enemy leave this behind? Only way to know is run on in. Maps themselves are serviceable but not totally standing out in any way, aside from Blind Watch which is one of the worst maps I have ever seen in any shooter. The main mode being control, the placements are just baffling here, putting A by itself on one spawn and on the entire other side of the map having B in some very close quarters room, with C being right beside it outside the window. The entire game is people rushing these points desperately trying to control both as without them your spawns keep shooting you back to A and everyone else can watch over B and C with ease without moving. It is obvious that this issue exists just playing the map two or three times, yet it somehow got playtested and exists in this state in the retail game. And again, random ass loot that doesn't seem curved to benefit actual skill.
so there's a few of the issues the game has. there's still more, like the lack of proper communication, barely seeing worlds populated, the tower being an awkward quiet zone where all you can do is dance with people or smack your face off a ball, etc. but I'll just stop here.