Interesting observations. I think the Celtics are generally a front-running crowd, in that they cheer loudest when the team is playing well. The crowd cheers loudly when we hit big shots, play great defense, score in transition, make big dunks, go on a run, etc., etc.
What the crowd doesn't do a ton is "pick the team up" when they're playing like crap. If the crowd is sitting there watch us come out flat, or in the midst of blowing a 20 point lead in the 4th quarter, I don't think the locals want to cheer and be super energetic.
Also, for whatever its worth, the energy of the Boston crowd is rarely reflected well on television. I don't know if it's acoustics or what, but it's rare on television that I feel like the crowd is absolutely electric. Going in person, though, you can feel that, and you see much more of the individual player love the crowd gives guys like JT, Brown, Smart, etc.