As already mentioned, it's pretty difficult to progress at the start. Slow movement with fast draining air and the relatively sparse air pockets felt very difficult. If there was just one of those three I feel it could be a lot better, even slow movement and fast air drain could work if there were enough air pockets to sustain us underwater, or something like air columns so you're not forced to swim all the way back up. Like the guy above, I grinded out the air tanks but I didn't notice much of an improvement and then proceeded to die.
Everything else tho is pretty good. Everything underwater is obvious at a glance, the ship looks amazing, and the music fits perfectly.