I didn't think Sideways was depressing -- it's pretty clear that Paul Giamatti's character had finally decided to move on with his life at the end, and that he hooked up with Virginia Madsen's character. It was a nice, thoughtful piece on a guy who, at middle age, had grown really uncomfortable in his own skin. It had some really great laugh-out-loud human moments, too, like when he -- a forty-something man -- steals the money from his mom's dresser, or the, er, "trailer love scene". Lowell from Wings gave a really nuanced performance as an unhateable narcissist, too; seriously, he was a prat, but how can you hate a dude who picks up fat chicks just because he unashamedly needs the validation? The unlikely friendship between him and the self-loathing Giamatti character was really well done.
Sideways was a really well-assembled, thoughtful movie that didn't try to play up the idiosyncratic nature of its characters, but instead balanced comedy and human drama quite well. Payne knows how to direct movies about outsiders in a sensitive, affectionate way without compromising their anti-social, often self-destructive natures.