1st series was great and easily the best, the 2nd was very good too in spots. 3rd series was disappointing for me (apart from the excellent Crimping and the Crab episodes). I still enjoyed parts of the 3rd, and it was OK overall, but it just seemed like Noel was playing himself and not the character of Vince, a little lacklustre IMO.
Boosh has some great moments, though I can understand people not liking it (aquired taste). The characters are brilliant. My favourites are The Ape of Death and Old Gregg, I'd say. Although Vince Noir is sometimes only funny in smaller doses but Howard's always great. Noel Fielding's other characters are very good (Old Gregg, the Spirit of Jazz, The Hunter).
Fave Boosh moment: The Legend of Milky Joe ... "The man's an arse"... Without doubt my single favourite moment of all the Boosh episodes. Genius.