Ok, so I know I've complained about games going down hill after the initial title. However, there are games that get better as they make new ones. My best example would be the Battlefield series. Remember the original Battlefield? Now compare that to Battlefield 2. Then compare that to Battlefield: Bad Company 2. They've made the game much better. Making more of a team effort kind of game. More so than Battlefield 2, because now you have certain classes with very specific jobs. Making a good squad unstoppable!
There are other games that are exceptions as well, but this is the best example I could think of. Feel free to mention some others!