A wonderful way to bimble about for a bit
It has to be said, Endless Oceans actually does come quite some way towards that state of mind, which is pretty damned impressive, I reckon. OK, so it isn't technically accurate - there's no worry of DCS, and as for encouraging you to TOUCH the creatures (no no no no no no no no!) it's a bit naughty. But, hey, I love playing Grand Theft Auto as well, and I've not car-jacked anyone yet. :-)
But the general ambience... pootling around, looking at lots of lovely fish and making the occasional wondrous find is pretty much what recreational diving is about. While the graphics may not be hyper-real, it can still make you go "Woah!" in a good way.
As a game, there's not really much to do per se... but as a way to relax (and learn a bit about fish)... I love it. Right down to the polar bear on the boat deck (although he did look a bit of a stoner, I have to say).
Ultimate accolade? My very experienced diving buddy who NEVER plays computer games was still happily bimbling around on this after four hours. If you want to try something a LOT different you could do worse than scour the second hand shelves for Endless Oceans.