I've never been in the Garden, of course, but from what I hear while watching the broadcast, it seems, indeed, that the Garden is not as loud as before and not as "rocky". It seems to me that the crowd only gets really excited on certain plays, like the Rondo fastbreaks or a couple of straight buckets while it got on his feet really easily before and helped the team step up its level of play.
I don't think you can blame the crowd for the team's poor performance at home, though. The boos, on the contrary, did help the team to step up and stop disappointing its fans.
Like jdpapa, I'm confident it will be another story in the playoffs. I've re-watched some late situations from last year's playoffs recently and man, the Garden was such electric and such loud that it was very impressive. Every bucket down the stretch made the crowd litterally explode, awesome! Can't wait to see this kind of support back in the Garden...