To start off with, let me say that I bought into the hype surrounding this game. I was totally excited to play it and bought it within a week of release...something I NEVER do (mostly because the price comes down a bit a few weeks later). The whole concept sounded fun and I generally like simulation and strategy games. Because I think of the game as several different games packed together, I'm going to review it like that:
Cell: Fun but monotonous. In this stage of the game you get to play a growing microorganism. You get a few parts to play with and then off you go. It's fun..for about 10-20 minutes.
Creature: To me, this is one of the two main parts of the game. Again its really fun for about 1-2 hours. Then you realize that most of the parts you can find are pointless. Theres really only 1 idea part of each type (ie theres one best mouth if you're a carnivore). The additional parts (ie nose, ears, etc) do nothing. Adding extra parts (for example you might want to put lots of spikes on your creation) have no additional effects. But building new and interesting creatures is fun for a bit.
Tribal: Boring. Fight or socialize with the other tribes to move on as quickly as possible.
Civilization: Fun for about 10 minutes, then..boring. Once you beat the initial rush and grab back and settle into a pattern, victory is just a matter of time. No skill is required here. Your buildings and vehicles are fun to play with at first...then you realize theres no advantage to the buildings (all serve the same function) and theres 10,000 other vehicles that you can use just as easily. At this point in the game I just stopped feeling like making pointless modifications (you could spend an hour making buildings, but why?) At least your vehicle's parts make some game play difference.
Space: The 2nd main part of the game. At first (like all the other stages) its fun..exploring the galaxy, planets, finding stuff, trading, colonizing. Then the constant pirate attacks and eco disasters begin. You'll spend 90% of your time flying back to some planet to fight off pirates. Or don't bother. It doesn't really matter too much. This part of the game can go on forever if you so choose. You spaceship is solely a design for ascetics. Theres no functionality to any of the parts, so do what you want with it.
The game play is pretty straight forward and well described. You're never confused about your goals or how to do something in the game. After you play for 5-8 hours that initial addiciton feeling wears off and you're not left with much. Theres no real story (well...a REALLY weak one) and none of your choices throughout the game have much of an impact on game play. The missions are monotonous to the extreme and trading is pretty slow to get started.
There have been some expansions...personally I feel that they should have been included in the game. Overall the game is ok, but I really resent having payed 49.99 for it when it came out. I'd say its a $19.99 game that you'll play for less than 20 hours.