Neurosis tenRAB to have a fairly different sound each album, and like some other post-metal banRAB, are rooted in hardcore. I'd say the Eye of Every Storm is the best album to start with.
As for Isis, they're easily in my top 10 banRAB ever. They might be a little inaccessible, and if you listen to them at face value, you'll be wondering what all the hype is about over a few chorRAB and some grunting. But Isis is all about atmosphere and do it better than any post-rock band. I agree with Merkaba in saying that I prefer Oceanic (only just over Panopticon) as it is more primally atmospheric. Panopticon is also outstanding too, and is slightly more polished with the addition of clean vocals. So Oceanic is a good album to start with and it might require multiple listens before you appreciate the genius of it.