I've been playing it non stop since Friday 18th. It's a totally amazing game. There are a few signs that the oublishers rushed the developers a wee bit though. For example - in the dynamic campaign, there are a very limited range of messages from HQ, there are no wolfpack operations with other u-boats, there are no re-supply u-boats, there are no static or docked ships in enemy (or friendly) ports (nor any nets or mines), and they someone neglected to give the players a method of drawing accurate bearings when using the map in 100% realism mode (i.e. when yoiu have to mark up all contacts yourself - the only updated moving map type thing being your own position).
It is wonderful though, and all signs point towards these features being added in a timely fashion through patches.