It's really interesting how they changed. In the N64 days they were to the quality of Nintendo titles, which was amazing.
When MS bought them everyone thought they'd bought the next best thing to the big N however I think there were already some cracks. It makes me wonder how much they were aided by Nintendo to make the games they made as the move swiftly highlighted a stark contrast in quality.
I honestly think MS saw them as such and gave them free reign to make what they wanted, so they went ham. Without the guiding hand of N what they produced just wasn't up to standard, so I'm not surprised that eventually MS needed to step in and put their foot down.
Don't get me wrong they're able to produce good games but none have been to the 'expected' quality.