Yeah, UL is my most played game too. Lumines a close second, with a sprinkling of my other games.
I'm playing through as an Alchemist as well, and while I like the Poison shot, I've concentrated on building up my Chain Lightning and what ever the spell is where you drop the explosive pots. I can drop three of those little land mines now, and chain lightning will jump to four enemies, so I'm pretty adept at taking out bad guys quickly. I think I'm about level 24 right now.
As I said earlier, it gets a little repetitive in it's game play, but still fun. If UL had mixed in some puzzels and more role-playing elements, this would have climbed up into the ranks of the best games at launch. Still, like I said, it's a lot of fun to play, and I agree that it is getting better the further in you play. I actually like the music quite a bit now, but some of the other sounds, and animations for that matter, get pretty repetitive.