It’s been a long minute since I’ve ran GURPS but I don’t recall any major changes between 3rd and 4th.

Since you mentioned it though, for generic systems I think I honestly prefer Cortex. I’ve played it with medieval settings, modern, and sci-fi. I like that it uses all the dice and frequently. It’s just more fun for me to roll more dice variety. They also have a fun system where you have two health pools, one for normal damage and one for stun damage that you fall unconscious if you run out of. I thought that was neat since it allows you to more easily play that pacifist role if you want, which you don’t see too often from my experience.