I'm mildly amused by the vitriol some people have for a man over sixteen or so hours of moving images. It's just... bizarre, really. There are better things to invest your sense of well-being in than a few movies.
That being said, as a fan of the original three movies (not a fanatic, thank you) I do think Lucas seriously botched the prequels. It seems to me that he's at his best when he's being thwarted from creating his original "vision" and has to find ways around the limitations placed before him. And it does seem to help if he has other creative, and more-focused, people helping him along. I won't deny that A New Hope was as much about spectacle and bombast as Phantom Menace was, but PM seemed more... compartmentalized. As if Lucas decided that THIS section of the movie would be whiz-bang special effects, and THIS section would be exposition and plot advancement... and then didn't really bother tying them together.
And then... there was Jar-Jar. Where C3PO was amusing for his bumbling about, Jar-Jar came across as annoying. Perhaps if he'd been given an R2-D2 type of foil of his own, it might have been better, but to be honest the movie could have gotten by perfectly well without him. His inclusion feels like Lucas came up with the idea to put a marketable sidekick in the movie and then followed the worst possible decision tree in its development.
Worst of all, however- and here I'm not sure how much of this can be laid at Lucas's feet; I don't know how much input he really had- was the casting. Ewan MacGregor was a fairly good call as Obi-Wan, and who hasn't wanted to put a lightsabre in Samuel L. Jackson's hands, but the twin mannequins that are Hayden Christensen and Natalie Portman absolutely sucked the energy out of any scene either of them was in. Having them together in a scene proved a miracle cure for insomnia, as they blatantly exercised their inability to emote or portray convincing characters. Christensen was particularly bad- he took Anakin Skywalker's slow slide towards the dark side, justifying every increasingly bad decision with the protection of his love, and turned it into an emo-tastic poutfest.
And then, there was the dethroning moment of suck [http://tvtropes.org/pmwiki/pmwiki.php/DarthWiki/DethroningMomentOfSuck]: "NOOOOOOOOOOOO!" [http://www.youtube.com/watch?v=Tim5nU3DwIE]
So, yeah, I don't HATE George Lucas. I never invested myself heavily enough in anything he made to be so deeply affected. But I do think he got far too involved with all the gee-whiz special effects and marketing possibilities to pay enough attention to things like story and characterization, and (as many others here have said) he didn't have enough people around him to point him in a better direction. I suppose when you spend a couple decades hearing people tell you what a genius you are, you can't help but let it get to your head.
[small]Oh, yes, I linked to TV Tropes. I bask in your hate! I feed upon it! Ahhh haha ha ha ha ha HA HA HA HA HA HA *cough cough wheeze* ...dammit.[/small]