I played D2 first, but after hearing everyone in the D2 forums go on and on about D1 my brother and I tried it. BTW - I only play PvE which means no Dark Zone. We’d leveled up to max (before NYC DLC) at the time.
There were things I liked about it, and things where I really missed the interface improvements of D2. However, what really kept me from spending a ton of time in D1 was the lack of loot. I remember finding a clever and hidden way to get up into a 3rd floor window and into an entire floor of a business, with multiiple rooms, closets, kitchen, etc. And there was practically NOTHING in there. Mainly a few pairs of pants and a hat or two. I couldn’t believe I’d found this secret big area and no weapons, no armor, basically nothing.
And it was there pretty much that way everywhere. Just not much loot to explore and find.
I enjoyed the battles, the gun play, but I never could find what was “better”. In the forums when I asked, OK, what is it all of you are talking about that makes D1 so much better? the answer was basically the Dark Zone is better and the replayable sewers.