Hmm... it really depends... I don't like it that much, but that's probably just because I've watched the episodes way too many times...
I think this would've been my favorite season if I had seen it before seasons 6 and 7 (yes, I watched the seasons out of order >_<). Dawn was awful in this season, she was just... ugh. Always whining and crying and being patheticly stupid and predictable. I mean, seriously. I loved the actor, and her acting, but... I really, really hated Dawn. In the 6th and 7th season, I think she got a lot better, and more, er, "confident" in herself. I think it helped that she finally stopped going on about being the Key, the only time that was mentioned... was... I think in Two to Go, by Dark Willow. And Dawn didn't even say anything then. In season 7, she was even better, and actually pretty useful to the scoobies. She did a majority (or what seems like) of the research, and she could do a lot more for herself besides whine. But, yeah, anyway, Dawn is a complete brat in this season. Just because she's the Key doesn't give her any priviledges to be so... annoying. Heh.
One upside of this season was Willow and Tara. That was very comforting, but kind of distracting... I mean, you hear people say "Oh, I like the 3rd season best because Angel's in it" or "I like the 6th season best because almost every episode has Spuffy sex" (which, ew, to that second example), which isn't bad or anything, don't get me wrong, but it doesn't have to do with the plot. People should like shows/movies/episodes/books/etc. because of their storyline. If you watched a show just for one specific thing, it would probably get very boring after a while of watching it just for that one thing. Example; in season 6, when Tara is shot, I have to admit that was very sad and it still often makes me cry, but I accept that it happened. Denial sucks. Period.
Wow, am I totally off subject.
Okay, anyway, my point is, the fifth season was [probably] pretty good.It's just that it's usually judged by one petty little piece. Dawn was not one little piece, though... she was like, the season itself. So to have that kind of a character stepping in and becoming the big focus of everyone, they have to be a good focus. (-cough- Good = no whining)