GURPS' basic resolution system is actually quite simple . . . until combat starts.
At that point, dear merciful heavens . . . .
I'll never forget the one fight when I was a player in a GURPS game that literally took 3 hours---and it was just a basic, run-of-the-mill fight between a party of 4 PCs and seven or eight lower-echelon swordsmen. Every single turn took fifteen minutes---"I'm using my tetsubo then burning two fatigue to activate this maneuver. Oh, and I'm taking the -5 aim penalty to go for the head . . . *rolls* I succeed."
*GM rolls* "He doesn't block you, let me roll to see if he can dodge." *rolls* "Nope, you hit."
"Sweet!" *Makes critical hit chart roll*
**Player and GM spend next 10 minutes hashing out just exactly what happens based on the critical hit chart, whether the enemy needs to make its Health roll to remain conscious, blah blah blah.**
This was the point at which I realized that the trade-off for "realism" in RPGs was overrated.