That's a difficult question to answer..
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Fall Of The Rising Sun Ultimate (FOTRSU) is still in Beta, it is worth playing however.
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Don't forget Webster's GFO Game Fixes Only Mod v1.1
http://www.subsim.com/radioroom//dow...o=file&id=1196
Webster's GFO New Orders Bar Menu For 1.5
< Essential mod added after the main GFO mod
http://www.subsim.com/radioroom//dow...o=file&id=1192
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TMOwTw 2.50 doesn't have some of the restrictions that TMO 2.5 has but does have the feel and flavor of TMO 2.5
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Don't forget RFB 2.0.
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Many people use the RSRD campaign with the above mods however it changes many aspects of the main mod you selected too. You will be playing RSRD instead of GFO, TMOwTw 2.50, etc..
Many people don't realize that TMO hs its own campaign with added traffic layers (Taters layers ; ) modified and expanded by Ducimus that is worth playing.
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There are offsite mods too. the
Guerrilla Submarines Spyron Mod is one that I enjoy. It is a campaign that can be added to Stock and most of the mods I listed above.
http://www.subsowespac.org/silent-hunter-4-mods.shtml
Happy Hunting!