Bmiler
This is by far the deepest in prog territory these guys had ever done. Backdoor Possibilities features the same lineup as their proceeding album, Plastic People, but now it's on a different label, Brain. This also happens to be the final release on the green Brain label.
Forget any references to Deep Purple and Uriah Heep like you do Operation or Hoodoo Man, what you have here is prog that has more in common with Gentle Giant, perhaps a bit of Yes or Genesis. It's a concept of a New York businessman named Adam Striver who faces the Grim Reaper at a subway, who takes him to a movie theater that shows films of his life. There is supposed to be a moral behind it, because Adam Stiver was supposed to be a corrupt and bureaucratic yuppie, and he's told to find a better way, but it's agreed the story wasn't well written and this "Backdoor Possibilities" (also called "Beedeepees" or "BDPs") that Adam is supposed to discover makes no sense, and it seem like it was unfinished. Of course, they could have made it a double album, but I'm certain having moved to a new label, that wasn't going to happen.
Much of this album were basically collection of suites. "One First of April" is this opening piece. Zeus B. Held's keyboarding might remind you a bit of Kerry Minnear, with lots of Moog and clavinet, with string synth. "Beedeepee" shows more of that Gentle Giant influence, and you really notice it in the "Childhood Flashback" section, with those GG-like vocal harmonies. You could swear it was the Shulman brothers singing this stuff, but it was Peter Foller and Bernd Noske. "La Ciguena de Zaragoza" is an instrumental piece, a jazzy percussive piece, with a spacy synth part in the middle. "No Time to Live" is another great example how much the band was now in full-on prog territory. There are some Yes-like moments in the vocal harmonies.
This album is rather underrated, even many progheads don't take too kindly to it, but I find the album great. As for the hard rock crowd: it is prog, so if that bothers you, go for their earlier stuff like Operation and Hoodoo Man.