As a latecomer to Mystery Science Theater fanhood, I'm glad that former head writer/host Mike Nelson is continuing to make bad movies enjoyable with RiffTrax. Being a longtime fan of Star Wars since seeing the first film at the age of six, I felt morally obligated to at least take a look at the new trilogy. With each passing film I was more and more horrified. Mike's rifftrax on the prequels got better and better as the movies themselves became more humorless and unwatchable. Some fans might consider the third prequel the best of the bunch, but for me, it's the worst. Luckly the rifftrack for that episode is the best of the three; it's the only reason to subject oneself to the film.
300 falls into that same category.
MST3K tended to focus on films that were so bad, hardly anyone would watch them. The show eventually ran into trouble when the very existence of MST3K increased the value of the rights to the films they were lampooning beyond the point where they could afford the rights to the movies. RiffTrax escapes that loophole by distributing only MP3 audio files, which they then help sync to your DVD of the movie by having a disembodied voice (named Disembaudio) do line readings from the film periodically. Files are also available to sync with NTSC or PAL versions of the film, and there's even a special Windows program that handles the sync for you if you're playing the DVD on a computer. If you don't already own the DVD of the movie in question, you can order it from RiffTrax.
There, of course, is the catch-22. Riffing is funniest on movies that aren't very good, or that you don't like. I've also listened to the tracks for the Bourne Identity and LOTR: The Fellowship of the Ring, which are films I like. At some point these tracks fall a bit flat compared to the others. So in order to get value out of RiffTrax, you have to own (or at least rent) the movie. But riffing works best on films you wouldn't necessarily want to own.
RiffTrax seems to realize this, which is why they are also offering a video on demand option. Perhaps what they really need is a deal with NetFlix.