not played dnd before, but expected that game will have big different in style, depends on your characters choice. For example (this what i expected), if you warrior and ranger, you can stun enemy for ranger's attack. or ranger have net\trap and it would easy for warrior to kill if it on enemy. But if you with warlock, he can fear enemy and you will attack for free with aoo. And all classes have unique skills, which make them interesting to play.
And i not waited dos3 here, but there nothing like this. Doesn't matter if you picked rogue, and your friend picked warlock or ranger or warrior. Difference only that one will apply hunters mark or Hex, or warrior will just autoattack. And only what you can do together is autoattacking same target. There no interaction between characters, may be cleric can heal and cast bless, thats all. 2 mages can do some stuff, but 1 mage and any other almost no.
Is it only EA characters straightforward (driud looks fun at least, with his roots and whip) or game not about party interaction\some combos?