I skipped training and handbook and just threw myself into a patrol in 1941 our of Manila - many things fell into place all at once. I must say I'm impressed with the control interface - it's far simpler and easier to use than in SHIII.
And of course the fact that time acceleration won't get as jumpy as it did in SHIII when coming near convoys or coast (at least not that I noticed).
And, lastly, I'm positively surprised how smooth the game runs, even on a 1.8GhZ AMD64 with 1GB of RAM and an X800XL - no problems at all with medium settings.
The bugs are gonna be worked out soon enough
Only gripe I've got is that I really, really would love to play as a Japanese sub commander *Sigh*