Both have their pros and cons. I do enjoy the weapon system in D2, like running two primaries and SMGs, grenade launchers and more linear fusion rifle options. D2 also has ledge grab which was something we didn't know we needed until we had it.
Meanwhile D1 to me had a lot better stories and action with more fun. I have better memories with D1 over D2. Even the strikes felt better, heck even doing patrol missions were way more fun. Going to the tower was a lot of fun, NPCs had things for us to do i.e. factions or even the gunsmith weapons.