The thing with the new Banjo Kazooie is that they have alienated their previous fans with the new approach. The game is nothing like its predecessors, which were very awesome platformers. Although platformers aren't as big as they were back then, a solid one could be released to huge praise (Super Mario Galaxy, for example). They could have had a huger hit on their hands if they tweaked the previous systems around and went with a traditional platformer instead of the current system.
Also, just because scores are decent doesn't mean that the game is good to everyone. While the game might be good, it doesn't mean that everyone will like it. They took an established franchise and did away with the old formula that made it successful, which is taking a huge risk in gaming, hoping that the name alone will sell a lot of units. They should've tried to introduce a new IP with the current BK concept, which wouldn't have alienated their previous fanbase.
