Wow. I've seen A LOT of films (documentaries, indies, Hollywood) and The Real Beach Boy is in my top 3 favorite films ever. Are you sure you saw this film?
I have to agree with your last sentence: I'd love to see HBO do a miniseries.
I watched it, and it was really good. I suppose as a fan, I look at the film in two ways: In terms of the content and subject matter, I found it quite good and intensely interesting. Obviously, Jon Stebbins' book goes into much more detail, but the doc certainly touched on a lot of things the typical BB doc hasn't, and we got to see and hear from people that need to be seen and heard from. In terms of this as a "film", it's a bit less successful, and that's largely not the fault of anyone I would imagine. It was a somewhat short made-for-TV documentary. The budget and time constaints only allow for so much. They had to breeze through some stuff, and I'd say the overall tone was a bit more indicative of it being a TV documentary. Also, as I mentioned, it's not a big deal at all, but the style of narration (and perhaps the choice of even having a narrator) also contributed to it having a TV documentary vibe. And that's okay; it was a TV documentary!

But no, I wouldn't say this is in my top list of all-time favorite films ever. I don't even think it was neccesarily the best BB-related documentary, although all of them have their problems and strengths.