I have to make a confession here. I am a big fan of GURPS, have been for years. In the 90s and early 00s, I played GURPS almost exclusively. I even did playtesting and writing for GURPS.
For that reason, I am always baffled when people say that GURPS is too complex, or too realistic, or not playable. I learned something very important about GURPS that makes it easy to play, easy to run, fun, and usable for any game type. Here's what you need to know:
You don't have to use all the rules! Most of GURPS is optional. Lots of combat rules are optional. Look at GURPS Lite. It is a completely functional version of GURPS that uses only a small portion of the rules. If you find that is not enough, can keep adding options until you reach a level you like.
As for GURPS books I think everyone will like, I suggest any of the historicals, especially GURPS Russia. Sourcebooks like GURPS Religion are a goldmine of information for creation religions and religious groups for any system. Technical books like GURPS Vehicle are more for hardcore GURPS Gearheads, but that's ok, because that is what makes GURPS fun fun for them.