I daresay SH4 will get its day in the sun eventually, after all, SH3 had its problems too when it was released and had some real issues when new, such as multiplayer constantly bombing out etc, but with patches and mods it has matured into a great sim, and the fact that it is still massively popular after quite some time is testament to that. Any real submarine sim fan will certainly look forward to seeing SH4 reach that stage.
But in the meantime I, like you, am enjoying SH3 more.
Chock