As I get older and find that all new music "sounds like shit" (if you don't get the reference, google the phrase with South Park), I sadly have to come to terms with the fact that I will no longer appreciate a good Weird Al parody song, because half the time I'm not even aware which songs are direct parodies anymore as I never heard the originals. But I DO still quite like his "style parodies," which are far more creative. In those, he mimics the general sound of a certain band (an older one that's been around long enough to have a distinct sound, that is) without directly parodying any particular song, and when it's done well it's kind of incredible (check out "First World Problems," his Pixies style parody, for a fine modern example). A straight parody can be amusing, but making fun of the general IDEA of something takes a little more finesse to work, which is probably why you don't see it done too often in movies.
One of the rare examples is Walk Hard: The Dewey Cox Story, which was directed by Jake Kasdan, produced by Judd Apatow (at the peak of his success), and written by both. While Walk the Line was clearly a big influence, it's not directly spoofing Johnny Cash's story - everything from Ray to Great Balls of Fire to John Carpenter's Elvis seem to have been studied by Kasdan/Apatow and used as inspiration for their scenes. They're making fun of these things, sure, but there's a genuine appreciation for them as well - something that is sorely missing from other modern parody films. The demon bastards Friedberg & Seltzer (and to a lesser extent, Marlon Wayans) have ruined the genre for this generation by stringing direct references along in something that could be charitably called a narrative, sometimes spoofing scenes from trailers for movies that hadn't even been released yet. These ____ Movie things, which just got worse and worse as they went, instilled the idea that a parody had to be directly translating key scenes from the most popular, current films, with the (for lack of a better word) filmmakers adding nothing of interest of their own and seemingly having no affinity for the original material.
All of that is a long-winded way of saying people probably just didn't "get" the joke Walk Hard tells so well*, hence the movie's sad box office failure. Hell, the movie nails the tone of these musical biopics so perfectly that you could mistake it for a real one at times. John C. Reilly is a perfect choice for the lead role; he's got proven comedy chops but is also an in-demand dramatic actor, with a genuine Oscar nomination and everything - if he didn't do this movie, it probably wouldn't have been long before he was courted for a real Oscar-bait drama telling the same story. Kasdan gets everything so right; the modern day framing device (complete with one of the film's best jokes - Tim Meadows explaining that Dewey has to think about his entire life before he takes the stage), the early tragedy (Dewey accidentally cuts his brother in half), the chance encounter that provides the first big break, the song burning up the charts ("despite only being recorded 35 minutes ago"), the failed first marriage, the ever expanding number of kids shown in the domestic scenes... they do not miss a beat. Not only do they offer plenty of direct, silly jokes, but spelling out how goddamn similar all these movies are is a joke in itself. The movie would be funny even if they didn't have so many great lines coming at a steady clip ("This was a particularly bad case of somebody being cut in half"), because it's just hilarious how many times we've watched the same movie with a different musician plugged into it.
And they don't shy away from the fact that Dewey, like many of the other biopic subjects, is kind of a terrible person. He's a bigamist, he steals his bandmate's wife, he doesn't meet most of his children until he's in his 50s, and he never once pays for drugs (not once). On that note, the inevitable drug dependency plays a big part as well, with Meadows (his drummer) always being the one to get him hooked on something after a very halfhearted attempt to keep it from him ("It's cocaine, and you don't want any part of this shit, Dewey. It turns all of your bad ideas into good ones!") Indeed, one of the movie's highlights, almost deserving of a movie of its own, is when The Beatles introduce him to LSD, with John (Paul Rudd), Paul (Jack Black), Ringo (Jason Schwartzman) and George (Justin Long, surprisingly faring best) bickering the entire time, usually dropping in references to their own songs ("Maybe your songs won't suck shit when I'm 64"). As can be expected with this cast and Apatow producing, there's a wealth of material - the extended cut is a whopping 24 minutes longer, and the DVD offers another 20 minutes of deleted/extended scenes (and, in a separate feature, a collection of alternate jokes), and I would happily watch what's likely an hour of footage from this sequence alone.
They're just four of the film's surplus of cameos, which thankfully refrains from using any real musicians as themselves until the very end, when an awards show brings them out (including a hilarious parody of Eddie Vedder played by Vedder himself). Jack White plays Elvis, but otherwise just about everyone is just another comedian that already had or has since toplined their own movie. Ed Helms, Craig Robinson, Jonah Hill, Jane Lynch... it's an embarrassingly talented cast. Hell, even a traditional hardass like Raymond J. Barry gets to be hilarious as Dewey's dad, who taunts him with "the wrong kid died" every time he sees him. Jenna Fischer is also quite great as Darlene, the Reese Witherspoon stand-in who joins Dewey on a few songs ("Let's Duet") and stands by him far longer than any reasonable woman should.
The filmmakers and Reilly (a master improviser, something they mention several times in the DVD's bonus features) also get a lot of mileage from having Dewey (who never once paid for drugs) go through musical phases that allows him to do "style parodies" of Johnny Cash, Elvis, Bob Dylan, Brian Wilson and others. He more or less retires in the early '80s, and it's almost sad when it happens, knowing we won't get his new wave, hair metal, or grunge periods. But still, that's a lot of ground to cover, and the soundtrack boasts a whopping 30 songs, some of which aren't even in the movie (or only head briefly in a montage or something). And the songs are good! The title track is rightfully covered a few times (the punk version is particularly on point), and if not for a few goofy lines "Beautiful Ride," the movie's closing song, could easily pass for a genuine "I'm probably gonna die soon" reflective tune from any '60s or '70s-era singer/songwriter still kicking. I also quite liked his riff on Dylan, with total gibberish lyrics ("Stuffed cabbage is the darling of the laundromat, the mouse with the overbite, explained how the rabbits were ensnared...") accompanying a pretty decent vocal impression.
Reilly promoted the movie by going on tour as Dewey**, an event I wish I was cool/smart enough to have seen (Devin was!), and it's a bummer that none of that footage is on the (otherwise exhaustive) DVD set. As I said, the songs are genuinely good (and full length - the movie shortens them of course but some are about five minutes long), and Reilly is a master showman, so I'm sure it was a terrific thing to see. You hear "actor playing songs from his parody movie" and figure it'd be obnoxious, but it wouldn't work without the dedication everyone put into the film's genuine approach; they took making fun of these movies very seriously, and it worked like a charm. If you haven't seen it yet, rectify that.
*Though at least it got a chance. David Wain's "style parody" of rom-coms, They Came Together (which is every bit as funny as this film) barely even got released despite an all-star cast.
**Who never once paid for drugs. Not once.