I got it. The Predator one is okay...one really cool medal takedown (hanging from a gargoyle through a glass ceiling...booyah). I LOVE the combat challenge, but GS, you'll probably hate it. It's just a "last as long as you can" thing (at least I think so, because I eventually always die) where you just get hit with huge waves of guys. Also, the crazy inmates are in this one, which can be REALLY annoying because throws and instant takedowns don't work on them.
Overall, neither is earth-shattering or anything, but both are free so I like it. If I had to pay for them though, I'd probably be disappointed.
Oh yeah, and GS, I don't know if you still have Gold (I remember you talking about not having it way back when the demo came out), but they're only available to Gold members (for now).