Big and ugly? Just beautiful in an odd perverted way.
But in all seriousness I think my fascination and others' is her guns and size. I mean think of torpedoing an escort in this baby then surfacing and raising hell with those guns.
Personally I'd love nothing more than to have playable Japanese subs. Talk about having a hell of a time surviving. Going against Allied DDs, having to run dangerous resupply/transport missions, and most of all....having the I-400 and getting in close to the US coast to launch a/c. Too cool!