TMO (Trigger Maru) - greater difficulty - ultra experience realism. Things like - Mk 14 torpedo failure reflects how badly they historically performed. Japanese escorts have a varied skill set. Some of them are so damned good they'll wear you out trying to evade. Some aren't so good. I like the authenticity of the U.S. uniforms and the rank distribution/promotion track. etc.
FoTRS (Fall of the Rising Sun) - Pretty ... very pretty. Lots of ships modeled (as in TMO). Not as hard a play as TMO. There's also some added internal compartments (officer's and chief's quarters and wardroom (forward torpedo in S class boats). Another worthy super-mod.
Those are the two I'm most familiar with.
