Well, I finally managed to download and play AOTD. The AI looks fine (more subtile escort, merchant ships trying to evade... I didn't test airplanes), but the extremly bad looking ships through periscope is a total game killer for me, I don't even know what course the targets have, I can't see only pixels on the sea surface....
So, you mainly play with the nav map screen, which I find not very realistic. Also, you can't operate hydrophone, which is a big flaw. It's also necessary to find proper shortcuts, because playing only with the mouse is a nightmare...
But indeed, it's a new point of view of Sub simulation compared to SH3, and it's a pity that SH3 is not an improvment of AOTD...