Well, the thing about BoS was that if you're going to make a spin-off that's completely different than the originals - it's going to need to have some actually redeaming qualities. Just as a game, I didn't like BoS (I actually had it pre-ordered back when it came out - I gave it a good two weeks before I returned it.)
Even on it's own merits, I just thought it was clunky to play. Enemies shoot at you from off-screen, for example (and when has that ever been anything but a big no-no in game design?) My real problem with the game wasn't that it totally broke away from the gameplay (it was just a spin-off - that's what spin-offs are for: is to explore the franchise with different types of gameplay.) Or that it really didn't feel very "Fallout-y" (art direction was just "off," as far as I was concerned.
For me, the nail in the coffin was that I wouldn't have liked it even if it was called "Apocalypse: Brotherhood of Metal" and was it's own IP and not a spin-off of the franchise. It was just a fundamentally-flawed game. There's plenty of better examples of that style of gameplay, using that same engine - The Bard's Tale comes to mind. It just felt like shovelware, to be honest.
EDIT - I might some day rent it again or something - sometimes I'm a bit masochistic with my videogame choices... Just to say I played all the way through it.