Guacamelee is a great game and so is Halo Spartan Assault. Crimson Dragon is also a good game. I've liked the lineup but until last month owned all of the games already. I will check out Strike Suit Zero.
I got Guacamelee just because it was free, but that's not an exclusive.
I just check it from time to time to see if there's anything i want. Do they have a release schedule for August I don't know about?
As for 360 (and xb1), I'll download anything that shows up as free just to tag it in download history. That way if I ever feel like playing it in the future, I should be able to download it free of charge.
I have passed on them. I think one problem is that they rolled out GwG within the first of the X1's launch. So they don't have the huge library of games to pull from, and it really doesn't make sense for them to give out full retail games this early in the cycle.