I love the Champions system. But I've never really run a campaign in it, and thus I have difficulty creating balanced characters for that system.
What I like the most with the system, is that you can simulate practically anything with it. If you can imagine it, you can build it in Champions. It's as simple as that.
However, that versatility is also the system's greatest flaw. House rules tend to crop up all over the place. A 250 pt character in one campaign might not fit another 250 pt campaign, simply because of differences in limitations and whatnot between those two campaigns.
Furthermore, though the system is quite fast in play - combat doesn't bog down, and research and footwork is easily determined by a few rolls of the dice, using the 3d6 mechanic that GURPS uses to determine success - the character generation part is a nightmare.
With complete control comes complete chaos. If you're a novice to roleplaying and numbercrunching, don't even think of creating a character with more than straightforward powers. Personally, though I consider myself experienced in roleplaying games, I didn't even attempt to run a campaign until I got the HeroMaker, an excellent bit of software that allowed me to have running totals of what I had done.
Even so, I had problems with multipowers - especially those nasty Variable Power Pools (VPPs). I still don't understand them quite .
But I do like Champions.