Spent some time with this yesterday.
Things I really like:
UI is excellent, I like how the inventory/menu system is done, I like that I can see how many rounds are in my holstered weapon, I like that I can see what skills my team has picked and if they are on cooldown.
Setting is great, weather effects and night/day effects look excellent.
Gunplay is good, I liked being able to suppress the A.I. while my buddy goes for a revive.
Weapon customization is fantastic, lots of options for how to set your guns up.
Player customization is fantastic. Even with only 4 skills in the beta it gives you a lot of options, especially when you can mod skills. Perks to come in the full game too!
Dark zone is an interesting concept, teaming up and trying to extract that precious loot when you see a group of rogues closing in on your position is tense and I haven't really experienced much like it.
Things that remain to be seen
How good and long the story is - The biggest downfall of Destiny was the crap story. It's uncertain how much content the full game will have.
What sort of end game content there is, what the max level is etc.
Is story loot going to be made irrelevant by the dark zone?