A few thoughts: I've seen this several times now over the course of a few years, and I still have no idea what I think of it. Ralph Bakshi was one of the most bold and original filmmakers of his time, but that isn't always a good thing. Using a bizarre blend of animation techniques ranging from traditional hand drawn to rotoscope and silhouettes, there's never a dull frame, but the weirdness can be a bit difficult. There's an odd balance of adult themes, childish humor, and slapstick (complete with BOING sound effects) that makes this a pretty uneven and difficult movie to fully grasp. Who or what is the target audience exactly? This sort of feels like 'The Black Cauldron' on acid. The ideas and designs are pretty awesome, blending fantasy and sci/fi wonderfully, and I don't think I can overstate how much I love the final battle between the good and evil brothers -- who are the main focus of the film. It's incredibly bizarre, but worth watching as a sort of '70s animated relic.
Who would I recommend it to? I don't know if I can answer this question. It's so specific, I can only suggest people go in with an open mind and try to keep up.