I got the Galactic Edition, and I'm glad I did.
Cell Stage is fairly simple, which I expected, and I ripped through it in about an hour or so. Looks and sounds awesome, but is fairly limited gameplay wise, but you are a single celled organism I guess. I think this is meant to be an intro or prelude to the game though really rather than a major gameplay area.
Just finished up on my first session now, nearing the end of Creature Stage, and this game is so freakin awesome. I'm not going to spoiler anything, but wow, there are some really cool surprises, and the game is starting to really open up with options now.
I am playing it on normal difficulty, and it definitely is not a pushover, having died several times. Creature stage is just so much damn fun to play. Deciding whether to befriend or attack neighboring creatures is fun and enjoyable. I don't think you can get by on pure aggression either.
This game is not COD4.