Felt like some GoW, picked this up. Played CoO before, my opinion hasn't changed on a second playtrough : enjoyable, but maybe my least favorite game in the series. It just doesn't stand out in any way.
Ghost of Sparta on the other hand! Man, RAD really knocked it out of the park with this one. Great pacing, good bosses and a pretty hefty challenge if you start on hard. What a bitch Erinys is. The game looks really impressive too, and there's a big variety of locales. I can really see myself replaying it at some point, it's just behind II as my favorite part in the series.
Props to RAD for creating the most fun non-blades weapons in the series. Santa Monica probably agrees, since they kinda stole the Zeus gauntlet for III. Loved the Arms of Sparta as well, used them as my main weapon once I got them.
One thing I noticed in Ghost was that they shied away from really big long battles with tons of waves, but just made enemies more dangerous (at least in hard mode) while keeping the numbers pretty small. It made for shorter, but more intense combat sequences.
They also didn't include many blade fodder enemies. Even the basic soldiers can rip you apart if you're not careful. Encounters, even early on, can be pretty intense.
My only big gripe with the 2 games is the dumb placement of checkpoints at times. As in : right before an unskippable cutscene. May not be noticeable on normal, but it is on hard. They did improve on this in GoS though.
All in all this is a collection that no one should miss. I got a feeling GoS got a bit overlooked everywhere, and that's a real shame.
Also part of the 5 GoW platinum club!