I like both DK1 and DK2 for their own respective quirks. I liked how creatures in DK1 would grow in size as they leveled up, I liked how you could fully summon one or more horned reapers so long as you created special little zones for them to live in and keep calm, and I actually liked how the workshop was handled. Yes, the workshop in DK2 was far more precise and would only build what you had a use for, but it also meant that you would have to wait for something to be built and your trolls would frequently be hanging around with nothing to do.
And I did like that things were made in the workshop, in both games. It meant you would have to sacrifice pure combat capability in order to make room for defensive traps, doors, and the like.
The trolls in DK2 have a very special place in my heart for being the disgusting, ornery, pathetically weak little dudes they were. Few things lightened my day more than watching that little snotskin waddling around on his secret business, grumbling and grunting all the way. Yes, so they were cut down by little more than a dwarf, but they were still lovely little dudes. And setting up a workshop specially constructed for use by bile demons, while it had its own appeal, didn't really have the same versatility as the troll's better movement.
I really liked the different environments in DK1. I was practically giddy when I came across the first snow levels. I also liked how slapping someone was really a very handy (har har) tool, unlike in DK2 where it didn't provide enough of a boost to make up for the slide and delay after hitting someone. Heck, in DK1, you could even set up an "autoslap" to whack all your imps and keep them working their little buns off. DK1 also had internal conflicts which, although a nuisance, added that extra little flavor to your dungeon.
I feel that both titles have their own strengths and weaknesses. Neither one is really a dungeon sim, but very few game devs are enlightened enough to view simulations of that sort to be as awesome as they are.
Or rather, I should say that most mainstream buyers aren't enlightened enough...