Not too bad of a system. It's kind of like old D&D but way simplified yet way complicated at the same time. I feel like the whole thing is more of a guide, template, or base to tailor to your own needs as opposed to a complete game. That being said, I used the system, with my own heavy adjustments, and had a great time.
I felt like the classes, skills, and race/species were a little too broad/open-ended so I tightened them up to less than 10 races & classes each with an equal number of available powers, and I came up with specific skills for my players to choose from. The original version I read was very clunky, almost hard to get through, this revision is a lot better.
In the old version, I had a hard time fully understanding the armor system, so I scrapped it and used my own, in which players had to roll a 1d6+x where x was some armor value on the equipment. The new, revised version made much more sense of it, and I'm still not sure how I feel about it, but it doesn't seem bad at all.
Now, my gripe, and why I only gave it 3/5: My group & I had a great time with this system, but I wound up spending so much time on having to tailor the system so that I felt it was balanced & consistent that I didn't get in as much time as I would have wanted on fleshing out the adventure. It was a homebrew setting & adventure, and having to mod Challenger so much I almost felt like I was creating a homebrew system as well.
Either way, the author obviously put a fair amount of time & effort into this, and for the price (free) it's definitely worth checking out. I liked it enough that I came back to check out the revision, and plan on using it again. A great tool for gamers looking for something loose, open-ended and fun. My thanks to the author.
[3 of 5 Stars!]