Hands down, the most disappointing game ever has to be Spore.
This game was hyped for over three years and what did it deliver?
Ok, the Creature Creator is great. No one has done anything similar. It is powerful and simple to use, and some of what people has put out is unbelievable.
But where is the game? The rest of it is so shallow so as to be some flash game made up but some teenager for a computer class project. I am not a big fan of The Sims, (although the wife likes it) but I prefer it to Spore.
Surprisingly enough, the best part of the game for me is the Cell stage (1st stage). Although a cut down version of Pac Man, it doesn't pretend to be anything else. The second stage, the Creature stage, also has some promise, but it quickly evolves into a very simple mini game of repeating the dances of other creatures or killing them.
Stage three and four (tribal and civilization) are equally boring, made worst by the fact that some more depth is expected.
Only the Space stage provides some gameplay. However, once you have seen enough of the stage and discovered the secret of the universe (more disappointment), the game is pretty much done. Even tweaking the colour, etc of planets gets boring. Do you want to put chocolate swirls or spirals on that planet? What colour should they be? Compared to the options you have in the Creature Creator, terraforming is a pale shadow. There is no reason to keep playing, as every planet seems to be only slightly different than the last. Spore tries to cover up this lack of depth with various achievement type discoveries you can make, but most will easily see through this.
Overall, great concept, executed with the polish expected of a Will Wright game, but no depth.
Spore is a huge disappointment.
Note that Spore: Galatic Adventures will soon be released. This promises to add various more missions to the space stage and looks to have some promise. However, too little, too late for this gamer.
Add your most disappointing game in the comments.