It varies, but overall I'd say it was a pretty good year.
Some sets were awesome (All vehicle sets, a good deal of Makuta, some Nuva), but other sets were tragically bad (Oh, Gali). The story was universally pretty good, though a bit less sci-fi in Dark Mirror would've been appreciated, and I think Greg handled the return of the Nuva pretty well. There were lots of fascinating parts that brought a legendary feel back to BIONICLE (Which was conspicuously absent through most of 2007), such as the Codrex, Tren Krom, and the infinitely-awesome Journey of Takanuva.
Not to mention the ending, which was incredible- What with Mata Nui awakening and Makuta appearing in the stars (That was certainly a part of the legendary feel) and Makuta destroying all the other BoM members. Plus the Ignika went from being a threatening, frightening presence to being a fairly likable character. And a lot of the Makuta characters were pretty cool, though I was glad to see them die and forfeit their title to the original.
Unfortunately most of the canister sets reused old designs without even 2009's excuse of creative use of pieces. This was a very big disappointment, and the simplistic small sets made it even worse... Still, though, many of the sets were decent in their own right (Onua and Lewa were pretty cool, for example), and the Phantkuta were all good, what with the new torsos and all. And the vehicles are awesome, but overall I'd say the sets haven't been 2008's strong suit.
Storywise, though, a definite improvement over the monotony of 2007, most of 2006 (The first half of that year was good, but then it faltered), and the sheer nonsense of 2005.