BRP in its various incarnations is worth a look.

Fate Core if you want a more 'cinematic' experience (and I can further explain what I mean by cinematic - you can have realistic cinema, after all). I'd definitely recommend Core over SotC.

GURPS is great, but can be heavy on the crunchy bits.

Burning Wheel is interesting. I'd actually recommend reskinning MouseGuard over BW, especially as an intro to the system.

Honestly, few games outside of d20-based ones have the incredibly amount of character advancement that you see in d20, if that's the major concern.