Games that start out good, but then get boring

I'm sure you have all played some games that started out pretty good, but then began trailing off and either became repetitive, or boring. Feel free to name some of those games in this topic.

The main game that made me think of this topic is Katamari Damacy. I really had a blast with Katamari Damacy at first, but after playing the game for a few hours, most of the levels started to feel the same, and even though it was upping the ante for every new level, it just starts to get boring.

I never played any of the other Katamari games. The first one was more than enough for me. Great music though..

I enjoy the Katamari games, but I find I generally will play them in one blast and then not touch them for a while, because they are repetitive (if addicting at the time!)

If I had a name a game I've had like that...well, really, I now feel this way about a lot of 3D platformers nowadays. I played through Jak & Daxter recently...while it was a good game, good platformer, that was just the problem. The core gameplay just did not evolve very much and the game was too long to not really change. It didn't help that the story felt a bit bare-bones and uncreative, with little in terms of character development. Of course, it did get harder later on, but sometimes harder just felt like a lot of cheap deaths and a difficult camera.