Shush, ourtime. We're not allowed to complain about how long it takes Adam Guettel to get a show out. I can practically hear the villagers coming to flame us now.
I don't think Adam Guettel has done anything to reinvent the musical theater. Myths and Hymns to me is more of a song cycle, Floyd Collins fits pretty neatly into the genre (although it is, musically, one of the most unique musicals, along with Myths and Hymns), as does Light in the Piazza. Whereas I think LaChiusa is really adventurous in what he does, theatrically. I don't dig his music as much as I do Guettel's, but I think LaChiusa is the more ambitious writer all around. Of course Guettel is mainly a musician/singer/actor, whereas LaChiusa is a playwright.
He is incredibly prolific, but then again this is his living. Guettel's a little rich boy ;P
Guettel has it pretty easy I think. LaChiusa is really ambitious, and as such he provides wickedly divisive work (some people love him, some hate him, some find him pretentious, some moving, etc...).
And really, Sondheim has said he wouldn't mind having a hit, so it's not like you can knock Guettel for not being experimental like LaChiusa is. You write what you want to write.
PS, I don't think the musical theater needs reviving. I think it's been revived! I wish Guettel was more prolific though

Well, we have the next few Lachiusa shows to look forward to next year!
yr ronin,
joey