Maybe what the world needed wasn't another guy buddy film.
Two guys going out on a road trip, drinking, causing trouble, and each running away from something in his life; I think this kind of thing has been done before. It hasn't been done this well before, though, at least not too many times.
To use the wine-tasting language ubiquitous in the film, it has deep notes of the The Big Lebowski, with a strong backbone of On the Road and noticeable overtones of Fear and Loathing in Las Vegas. And I'm not sure, but I think I detect the slightest taste of Animal House and an earthy after-hint of Barton Fink.
I felt the presence of The Big Lebowski most strongly. It was hard not to see the two protagonists as reincarnations of The Dude and Walter. One of them continuously fucking up, getting the other into trouble, and apologizing profusely, as a series of unfortunate deceit-driven events relentlessly unfolds.
There's nothing to love about the characters really; unless you love to pity people. I do enjoy movies about depravity. I especially enjoy stories about depraved artists, struggling to make a living from their art and feeling as if the world does not understand them. It's an interesting archetype in U.S. American culture, one that tends to excuse us from actually evaluating artwork; instead, we just find ways to make the life stories of the artists interesting, and focus on that. It's interesting that the myth can make for such popular stories, but our treatment of artists remains just as poor (and actually seems to be getting poorer over time). We still neglect to carve out a place for (at least certain kinds of) art in our economy.
In this case, the artist is a writer, who may be very good or very bad. The only encounter with his work in the movie is a convoluted description of his project, a novel, to a woman he's interested in. We never actually find out if it's any good. It doesn't matter. What matters is that he drinks a lot and is really interested in wine. Actually, the other main character is an artist as well, an actor. We get that he's been in some bad commercials lately, and that he mainly seems interested in using his soap-opera-star past as a way to impress young waitresses; but, like his writer friend, it's unclear whether he has any actual talent or not. What is clear is that he is getting married and having a very, very hard time with that.
Some critics have said that this film received some unjustified praise because it glorified the critic. So the critics returned the favor. At least, the ones who did not point out this reciprocity did. There's some truth to that, I think. If you consider yourself a knowledgeable critic in some area of art, entertainment, or food, you probably will get some more enjoyment out of this movie than someone who looks down on those snobs. The wine-tasting scenes, for someone who does not appreciate compulsive attention to detail in some form, may seem pointless and a little ridiculous.
I liked the film because it touched on a few topics that are dear to me; friendship and nostalgia, alcohol, road-trips, writing, existential crises, and being a critic. If you're not interested in any of those things, or if you need to respect/like the protagonists in movies in order to enjoy them, Sideways probably should not be at the top of your list. But I suspect you'll still get a few laughs out of it, at least.