If SH4 is on the same lines as 3 (except being in the Pacific mind you) then the sim will be even more enjoyable. After all the allies did win and I feel playing a sim from the winner's perspective would be refreshing.
The last 2 sub sims have been about the nazis.
The more a read about how the Germans had the best planes and the best subs and so on and so on.....the more it reminds me of those folks in the South who are always engaged in reenacting the Civil War.
BTW...I live in the South....Been there done that.......