I was initially drawn to GURPS in the early '90s after playing D&D for about a dozen years. I loved D&D-style fantasy gaming, but my players and I were chaffing at the class/level system. I'd played GURPS a few times with other GMs and thought the point-buy system with advantages, disadvantages, and skills was both elegant and powerful. I enjoyed the way you use disadvantages and quirks to build a flawed character and how you can adjust, replace, and evolve these over time to reflect character growth and change. I loved the fact that I could create pretty much any character imaginable. I recall in the early days having a blast with my players just coming up with different character concepts. It seemed magical that we could start with a cool story and then build a character out of it.
I don't know why I'm using the past tense because all of this has largely remained true to the present day. Just yesterday I had an extended conversation with a colleague who has recently gotten into GURPS about some character ideas that he was bouncing around. My children and their friends have had a blast designing all sorts of wacky characters from She-Ra to a dragon to a mermaid to a bunch of faeries armed with pixie dust.
Unlike some, though, it's not really the gritty realism that draws me to GURPS. Nor is it the potential to run so many genres. I've been mostly running D&D-style games ever since I first started gaming. (I play in lots of other genres, but as a GM I've stayed in my happy fantasy lane.) People sometimes ask why not just play D&D. I've purchased and played (extensively, sometimes) each edition), but I always turn back to GURPS. For me, ultimately, GURPS does what I'm looking for in a fantasy game better than D&D.
For my first big 15-year GURPS campaign, we totally ignored most of the advanced combat rules. Since then, most groups I've played with have wanted to use some additional options like hit locations and whatnot, but we don't let it get too bogged down. It is, however, comforting to know that there are options for just about anything that we could ever want to include. So, although I have never rolled the dice to see if someone's glasses fell off, I think it is kinda cool in a nerd-cool way that that could be an option if we were playing that sort of game.