As a
Man in Black I demonstrate GURPS quite extensively, and I've had some feedback on what players seem to enjoy.
That tends to be: fairly normal people, with power scales from the realistic to the moderately cinematic. They get into situations over their heads, try to work out what's going on, and then deal with it. My games are often set in the real world, perhaps with some additional weird powers – I've done one-shot games with 1960s psionics, with modern magicians working for the government, with a modern militia group in the US as the zombie rising starts, and with 17th-century pirates and their ship's conjure. Even if someone has magic, very few characters (PCs or NPCs) are so tough that being shot with a pistol won't spoil their day.
I don't tend to run genre fantasy, because there are lots of other games out there which can do that already, and frankly because I'm not all that enthused by it. (At least one of my fellow MIBs
does do this with Dungeon Fantasy, and gets good feedback from his players.)
I like about GURPS: that I can have "normal people" who are easily differentiated from each other. That what most other games would relegate to personality notes have a real effect on gameplay (as mental advantages and disadvantages). That, in spite of all that, when I
do want something hugely powerful, the system is there to cope with it and doesn't break under the strain. That when I want to build a fantasy or SF or horror setting, I have books crammed full of advice on how to do exactly that.