I don't think it's linear, there's a lot of playing styles...
I remember my first run through the game, I played completely socially. I was afraid of dying.
I was attacked by angry lizard creatures, and that was the only time I fought.
The Creature stage is fine for me, but I think other stages shouldve been more thought out, such as the Cell Stage.
Theres a total of like 5 parts you can get for your cell.
Tribal stage; Eehh... Could use a bit more stuff, and not take a total of 10 minutes to complete.
Civilization stage:
Really
This is terrible
Why are you inable to have ground troops other than tanks that shoot the same generic missile over and over?
Space stage:
I actually really like this one
And theres my opinion in a nutshell.