Saw it opening night and thoroughly enjoyed it! It works for the same basic reason The Room works, which is that Tommy Wiseau is an amazing Alan Partridge/David Brent-style comedy creation who just happens to be an actual person. This movie takes that character out of his own wacky universe, sets him loose in the real world and lets hijinks ensue.
I gave Ed Wood a rewatch the day after for a kind of compare and contrast. They make good companion pieces because even though they have the same basic themes - friendship and creativity as expressed through terrible movies - they go about it quite differently, and Ed Wood as a character couldn't be more different to Tommy. Ed's a charismatic go-getter whose only real flaw is having no interest in quality. Tommy's an alienating weirdo who only really gets anywhere because he has money.
I don't know if it's as good overall, but it's laugh out loud funny and pulls off a similar trick of adding a bit of pathos to the story of a ridiculous movie. Plus it has one advantage in that Wiseau's redemption as a cult figure happened in his lifetime, where Ed Wood couldn't really avoid the downer that was the last years of his life.
One detail I noticed was that Apatow was slagging off the Star Wars prequels at his dinner table before Tommy interrupts him. I doubt they put that in there by accident, but was it to take a shot at Lucas, or suggest he's another guy putting himself out there only to get flack for it?