I played DK1 when it came out and liked it. Is there a good reason to buy DK2 when you can play DK1 over again?

DK2's main saving grace, imo, was the Pet Dungeon. I had a lot of fun just building the perfect dungeon in those, especially using the official editor to tweak a few things. :) The main campaign had moments, but for me at least, DK2 had nowhere near the same level of multiple strategy elements and re-playability as DK1. The combat pit for leveling minions (training room only gets them to lvl4) was a decent idea but during actual campaign gameplay was too much trouble to bother with - just toss them into battle instead. The "stun when you drop" was mostly pointless, since all you had to do was just drop them a little further away.

DK2 looks nicer, of course. And some of the feature tweaks were nice - eg, being able to build a 3x1 room that was functional because it was against a wall and had "furniture" was cool, and I liked the minion fear level feature. Funny to see them run away in a panic, sometimes. Some different creatures too.

I know some who prefer DK2, so ... as always ... your mileage may vary. :)