GURPS the system is kind of meh. It has only four base stats (strength, dexterity, intelligence, and health) which is not a *bad* split, but it has little concept of specializing them other than through a fairly hodgepodge system of skills and advantages/disadvantages. I say hodgepodge because while there are _hundreds_ of these skills and traits, with various worldbooks adding more, their quality is very uneven. The system itself is 3d6 based, which I actually like -- nice bell curve without ridiculous amounts of dice, but unfortunately resolving many actions can involve ridiculous numbers of _rolls_. Combat is especially egregious with this, where combat rounds are one *second* long. I'm told 4e has streamlined this somewhat, I'm speaking only from my knowledge of 3e (I started doing GURPS just before 2E was printed. Fond memories).
What GURPS mechanics are good for in my opinion is providing a mostly "normalized" system for incorporating all kinds of different worlds into; by normalized, I mean you get a good idea of how much a certain skill or advantage might be worth relative to others, based on their CP value. With its single 3d6 scale, you even stand a pretty good chance of modeling them mathematically if you're so inclined.
What GURPS is great for is the quantity and technical quality of its "worldbooks". None of them provide a compelling background story anywhere, just a technical treatment of the genre that you can paint your mythology or history over. Gurps Space is a definitive study of all the different approaches you can get for Sci-Fi, and has an awesome solar system generation system based on actual scientific models (where the distribution of rocky planets, asteroid belts, gas giants would be based on stellar mass, etc). Gurps Magic is by itself extremely bland, but provides a fun toolkit for different magic systems, including things like rune engraving and casting or improvised cantrips.