I have to say, the micro-organism stage seems to be the most immersive until you get to fly a space ship. The creature to civilisation stages are easy and repetitive, I found flouting around in the primordial soup a lot more interesting to be honest.
Not only do you have more enemies, but the combat is a lot more tactical as constantly tapping the attack button won't always win for you.
Shame it won't let you make micro-organisms, I don't like the early creature stage as much.
I heard that EA got Maxis to pull underwater settlements and civilisations for the obligatory expansion, so I hope the body drag feature will be implemented too.