So, after no-lifing it this weekend playing Destiny on PS3, I can say that I will be playing a lot of this game come release. If I'm able to have that much fun on the "worst" version of the game, then I know I'll be glued to my screen with the other platforms.
I love the higher focus on co-op, because that was something I've always found a bit lacking long-term for Halo. So that aspect has already greatly incentivised me to buy the DLC and expansion releases. The challenging higher level story missions are a lot of fun, even solo (I have no friends on PS3, so I played by myself most of the weekend). I'm a big fan of the AI and encounter spaces in the story mode. Not sure about explore or strikes AI, but it didn't feel as challenging, maybe due to network reasons or having other players dropping in-game.
ADS works. I'm still more of a fan of Halo-style, and I wish there were weapons that implemented that more traditional scope-style, but ADS works fine here. The movement penalty is negligible to me (at least with warlock), and the hip-fire is actually viable. I got plenty of kills in closer range using the hip-fire. I've never really played CoD, so the only other ADS shooters I've experience with is Battlefield on PC and Borderlands. This mashup is better than both. In fact, this is basically a Bungie version of Borderlands with an actual compelling universe and PVP mode, and to me that is a VERY good thing.
Respawns/Checkpoints when soloing are pretty brutal on the higher difficulty when under-leveled, they send you quite far back, which I actually like a lot! It reminds me of Dark Souls, since even letting a weak enemy get the jump on you means death, you have to be playing well the whole time or face that punishment. And it also uses death and ammo penalties as counterbalance experimenting to find what works best for a particular encounter, which I also like. I'm actually a fan of the higher level enemies having a lot of health - it forces you to learn their patterns and weaknesses, and you can't waste any time not getting those critical hits.
I do wish they would tone down some of the infinite respawning in certain parts of the game, though. It gets to be a bit frustrating especially on the Strike mission, because some players prefer to stay back and snipe the Devil Walker, and not focus on the enemies at all, so it makes it not very fun for the players who prefer close-medium range combat like myself.
Crucible was a blast for me, as well, once I learned how the Control gametype worked. I think it would work in Halo as well, where the more territories a team controls, the more points are awarded per kill, rather than a steadily increasing point score for controlling the plots.
The PVP game isn't Halo, and besides all the player customization stuff spanning into the mode, I find the maps to be simpler and a bit more arcade-ey than Halo maps. Instead of weapons and powerups littered around the map, you have special ammo and occasional heavy ammo crates, which are tied to your choice of "loadout" (which you can actually customize mid-game, which I also appreciate for experimentation purposes - what works in one mode may not be ideal in another for you). This simplifies a lot of the movement and learning the maps, but at least in Control, there's still a certain Bungie-esque "flow", with no real dead ends that I could notice - multiple entrances to each location, which keeps you on your toes - not to mention the shortcuts and movement options for each of the class' special jump abilities. The faster-paced nature of the game fits pretty well, but I doubt we will be seeing any more focused arena-style gameplay like in Halo, so there's not much competition on that front. It's different, but familiar. Bungie's description of "more lethal" is pretty accurate from what I experienced. The Iron Banner (where loot/stats matter in PVP, normally it's flattened for the most part in other modes) will be really interesting to see once the full game comes out with all the high level loot and gear. I mainly rolled Warlock, but it seems a lot of people have their own wildly different opinions on which class or gun type is "OP" so that's a good sign of pretty close balance (as is reasonable for a loot game of this kind), to me.
Between this and MCC and 5 beta, I will have a very busy few months beginning this September, and I'm happy for it.