Yeah, the biggest issue I had with D2 when it first came out was how disconnected it felt. It never felt like a full world, it felt like you warped into a map and killed some things with no larger goal, just some "kill x things" or "pickup x drops" mini quests. Then you warped back to base and then picked a new zone to warp to for no particular reason.

D1 at least had a story that propelled you forward, including tons of lore (admittedly poorly implemented lore, but it was there!) and secrets and easter eggs. The story and voice acting was one of the big criticisms at the start so it's one of the things they worked hard on fixing over the life of the game. So it was REALLY off-putting when D2 went back to no story and lore. (And as I said, they decided to fix it by just putting in the story from D1.)

Thinking on it now, Avengers had that same disconnected feel as D2 once you got thru the campaign. I quite enjoyed the campaign but the game stopped being fun after that. Coincidentally right when it started being like D2.