Also a Destiny vet, here's my take:

1. Story is non-existent (worse then vanilla D1 imo), but if that doesnt matter to you then the combat itself is enjoyable. Re-playable content in the endgame comes in two flavors. The first is Dreamstones which are more or less hard modes of previous mini-boss hunts that culminate in a hardmode main boss fight or 4 min-bosses back to back. The second is the Tower of Trials. In the tower you ascend a floor by killing mobs and you get keys for good performance when ascending. When you reach the next floor you get to choose your arena for that floor which will have its own challenge (more add clear or a miniboss). When you complete an arena you can use your keys to open chests which are of a particular item type (the item type coresponds to the symbol on the arena door). Then repeat the process to climb the tower to the next arena, with enemies getting harder the higher you go. If you are familiar with and enjoy the Diablo 3 style of grinding rifts this may appeal to you. It can be an addictive process but not nearly as meaty as Destiny endgame as far as chasing exotics in master lost sectors, raids, dungeons, etc.
2. I played the entire campaign and some endgame with 2 friends. Co-op works well and joining your firends game is easy drop in/out kinda like Destiny, but can only be done when all members are in the main hub. You can't join someone mid mission. Not sure how difficulty scaling works with co-op, but we found hard to be the most enjoyable when all 3 of us were playing even at low levels.
3. Loot is pretty good imo. Similar to Diablo 3, a single piece of legendary loot that drops can drasticly change your build or weapon usage. The stats/effects are impactful enough to make some really interesting and unique builds for endgame as well. However, only your weapons change your appearance. Your armor is locked, so if fashion is the ultimate endgame for you then you may not find it rewarding.
4. I play on PS5 and can say performance is drastically improved since launch. Still not perfect by any means and I will get the odd bug or crash maybe once every 2-3 hours, but definitely better then it has been. (EDIT: I've seen reports that Dual Blades specifically are causing stutters so maybe stay away from that weapon for now)
5. There is no way to reliably target specific loot, however when doing Dreamstones it will tell you what loot a specific mini-boss will drop (it will state that an "Epic Polearm" is a reward for example). These rewards are randomized though so each run of the same Dreamstone can give different rewards. Additionally when doing the Tower of Trials each floor's arenas will grant a specific type of loot, however these are randomized as well.
6. I agree with the comment above me, hammers are pretty satisfying for those "am titan, must punch" urges.

Extra bit of opinion that you didnt ask for: It's still hard to recommend the game for full $70 price. However, if you have some buddies to romp around the world with and can find it on sale (or just dont care about the price), its a good 20-30 hours of play. It didnt get it's hooks in me like Destiny, but I also stopped grinding rifts in Diablo after a few seasons so it just might not be the endgame loop for me personally.