Personally, I liked D2 better than D1. D1 was original, but it was basically just a dungeon crawl. There was very little variety to the environments. I enjoyed the outdoors parts of D2 as added "spice" to the dungeons.
Of course, D2 was an improvement over D1 in many aspects. No question. The diversity with the different levels was nice, even though, as the talking Elephant (

) said, the atmosphere was not as intense as it was in D1. It was a lot more arcade. I still played it a lot, so it wasn't half-bad, it just wasn't as good as it should have been.
D1 was simply the better game overall (when you compare it on a fair level, not directly, but with what was possible at that time in mind).
In D1 you actually needed tactics, in D2 you just needed better stuff, do more damage, etc. The difficulty scaled by how much more damage the monsters did, and not much else. That's an exaggeration, of course, but hopefully you know what I mean.
In D1 you could do some absolutely ridiculous stuff... like kill Diablo in Hell at level 30 (solo, including getting there; I still have a screenshot from that, heh), which wasn't nearly as tough as what some guys did... a party of four warriors with ZERO magic (no spells, no magic items, nothing; just healing potions and white equipment) made it through Hell and defeated Diablo (this took *veeeeery* long). Stuff like that is completely impossible in D2.
But the worst thing about D2 was... it ruined the fun in D1, because you wanted all the improvements with the style of the old game.
Now, if they manage to put the best of these two together, that would be awesome!
The gameplay vid definitely looks interesting (and the little subtleties, like the breaking furniture and the bodies flung off the bridge, or the goons climbing the walls in Moria-Orc style are very nice), even though Barbarian isn't exactly my favorite character there, and I didn't watch the other one (Witch Doctor).
Bye
Thanee