A nice, well-rounded and flexible game.
The first stage is cell stage. This is similar to Pac-Man in that you go around gobbling veggies or meat, depending on your pre-chosen diet. You can change from herbivore to carnivore easily in evolution mode in the cell stage, but it becomes slightly harder in the creature stage. You build up DNA in this stage until you grow a bigger brain and move on to creature stage. The simulated time in this stage moves in scale of 100s of millions of years. If you can get through this stage quickly, it drastically reduces your overall evolution timescale. I haven't explored whether or not it matters how fast you evolve, but it's still fun to see how fast you can reach space stage.
The second stage is probably my favorite - creature stage. This is the last stage in which you can change the anatomy of your
lifeform, but there is no hurry to leave it. It is basically a RPG as far as gameplay is concerned. It is limited in that you can't really upgrade your ability that far. There are 5 "levels" of each ability, and adding multiple items won't increase an ability in most cases. This is really frustrating when you have tons of DNA to spend; adding parts just becomes cosmetic and kind of pointless. A better ability upgrading system would really help when trying to battle epic creatures. At your strongest sub-stage, you are usually stuck with a party of 4 creatures, all with HP at 100 or so (unless you pick up a rogue @ 250 HP). That may work for other opponents, but the epics are at 1000 HP and do death blows with each strike.
The 3rd stage is tribal stage. This is where the RTS part of the game starts. Your creature is stuck as far as biological evolution, but can now wear clothes with special abilities. I would compare this stage to Warcraft games, although there are more social options and peaceful solutions, depending on your creature's survival and social styles. Once you conquer or ally with all tribes, you can progress to city stage.
City (civilization) stage is basically equivalent to present earth technologies (technically we're early space stage...). Your success now depends on your technologies. You have to build land, sea, and air vehicles that are focused on your city's style. Each city has its own purpose - religious, economic, or military - and you have 3 possible classes of vehicles that correspond to each city class. This part has a little SimCity thrown in, in that you have to build a city that balances entertainment, industry and residential buildings and make sure they are connected properly. Like the tribal stage, all civilizations have to be conquered or allied with to proceed to the next stage.
Space stage is the final stage, and the only stage with a really static storyline. The storyline centers around the Grox, which are a powerful civilization at the center of the galaxy. You are limited to intra-galactic travel, but it as immense galaxy, and few players will ever explore even 5% of it and all the planets therein. I would liken this mode to Galactic Civilizations, or SW: Empire at War, but you play as a pilot for a single space ship. You really don't "win" this stage, but there is a nice reward for reaching the black hole at the galactic center.
The best part of Spore is that you can start an any stage, so if you only want to play one stage, that is all you have to play. You aren't forced to go through all the other ones first. This adds to the game, and makes it like 5 games in one.
I would recommend this game if you like role-playing games, pilot games, or real time strategy. It is also good for just designing buildings, vehicles or creatures, as the designers are very flexible.