I did, and loved it too.
If you like it now and (I presume) haven't finished it yet, just you wait. It'll blow your mind.
I'm right at the end of a "regular" playthrough...I've spared bosses but killed many regular enemies. (Don't know how far you've played, I don't want to spoil anything for you) I've tried not to spoil anything because I've enjoyed it so much, but I played the demo like 5 times, and from that I imagine that there will be alternate endings based on killing everything or killing nothing. Not sure what I'll do about the fact that the game remembers everything yet, but maybe it'll still work. I'm gonna try NOT killing anything next.
True Pacifist ending: Don't kill anyone, befriend Papyrus, Undyne, and Alphys (only possible after getting a neutral ending, you'll need to get a letter from Undyne to initiate this), and clear the True Lab. Note: You can do this without starting a new game as long as you haven't killed anyone, just load after getting the neutral ending, then fulfill the conditions for this ending.
Genocide ending: In each area, kill every single encounter until no one pops up on random encounters, and kill all bosses. WARNING: Will taint future true pacifist endings... Unless you tinker with the game's save files (and probably registry entries). ;)
Based on story so far, Flowey seems to just be a jerk so I decided to kill him. Sadly, it doesn't seem I can reuse that file now to replay the final battles and see what happens if I spare him. :-/ After he closes the game it restarts normally instead of Flowey's way.
A little something for the steam version players who want to get rid of the post-genocide files the easy way. (http://fucknohtml.tumblr.com/post/133037946850/do-you-own-the-steam-version-of-undertale-do-you)