Getting back to Hamburg can be problematic if you wanna stay late.
Did it back in 2008 with a few mates. We couldn't be arsed to camp back then because we were continuing our holiday for 2 more weeks in the netherlands and spain.
Going to wacken was no problems, train to Itzehoe and shuttle bus from there.
Home though, that's another thing...We were kinda drunk, only remember getting back to Hamburg 2 out of 3 nights. Once we paid some fella with a car 50ish euro to drive us 4 people back to Hamburg. Second night we got a lift with a bus full of finnish metalheads who droped us of somewhere in Hamburg, after some time not finding our hotel we took a cab 200m
Third night I have no idea how we made it back.
I'm not as young, nor careless anymore so I wouldn't do it again.