mm324: Whether it's video games or movies, sequels usual aren't as good as the original.
Actually, with games there is a surprisingly high number of them where I consider the second installment to be the best in the series. I've also developed a theory as to why this should be. Here's the scenario I envision:
Someone has an idea for a new original game. They have a clear vision of what they would like it to be, but in the world of AAA games development there are schedules, budgets and time constraints involved. Often they are forced to compromise on their vision in order to get the game done on time. However, if it is good enough and sells well enough, a sequel may well be greenlit from the higher-ups.
So they start working on a sequel, only this time they're not starting from scratch, but have the first game to build on. Hence, the second game becomes the game they actually wanted to make in the first place. It's like the first one, but with all the wrinkles ironed out, and with a few extra features that were a part of the original vision, but didn't make it into the first game. This sells even better, being simply a better game. So a third game is greenlit.
Now they have to make a third game, but they have now fulfilled their original vision of what the game should be. However, they can't just make a game that is the same as the second one, so they have to make up some new stuff to put in it. This sort of pointless innovation, change only for the sake of change, does not necessarily make for a better gaming experience, and the third game ends up being worse than the first and second games.
So the series starts going downhill from that point. Sometimes it may bounce back, if someone with a new vision takes over.