It's incredible. 5 huge RPGs with faction systems, true choice and consequences, Deus Ex-inspired level design where every problem has multiple solutions... I played a bit of the first to get a feel for where it came from, and now I'm 15 hours into the last game, because I figured if I only have time to play one, I might as well see the ending through. All of them are jumping on points, so you can start wherever you want, although if you're going to play more than one, you might as well go for the first.
If I wasn't so far in, I'd just go back to the original. I will definitely play through all of these on and off for the next few years.
EDIT: Diggler41 is actually the guy who gifted these to me. And I didn't originally ask for them, I just pointed out that somebody else didn't say thanks for the key they used. Then he offers me a key in a PM. Thanks again, dude. Two of the best gaming experiences I've had this year were from generous gaffers (thanks again for The Witcher 2, Felix Lighter!).