I've been playing it for some time now and am greatly enjoying it. There are a few bugs and problems (aircraft spawning!) but looking at the development history of Atlantic Fleet I'm sure they will be fixed soon.
It feels a lot like the original RSR, which is is what I was hoping for. If you're a subsim nut like me, get it now! For the general audience I'd suggest waiting for the next 1-2 patches.
EDIT: the devs have already reported that the aircraft bug is fixed and will be part of Version 1.01.