Drop the Gato for the U-Boat - You'll be much better off. Trust me.
Now that SH4 has been out for a year now and patched four times I have come to the conclusion that its the same game as SH 3 was but in a different uniform and sub. I knew that there is something to be said about stalking a merchant silently under about 10 -20 feet of water hearing the sonar clicking and your men becoming excited. I also knew that even though Im a American it was not the same sinking *** ships in a Gato - I don't know why but it's just not the same maybe because its more fun for me playing as the under dog and the bad guy as playing for a country that had the war won in the pacific after Midway.
Now they have added content in the form of a new campaign, updated interface that makes it easier to get around, new subs, ranks and metals to boot. Your still not the Atlantic terror as in SH 3 and being in the Indian Ocean has a slightly different ring to it than the English Channel had but the trill of the kill has made it back in the game.
For $9.99 and some extra disc space you can't go wrong here and if you still haven't made the switch to SH 4 now is every reason in doing so. Try it and you'll be amazed how good it feels once again to stalk and sink your fellow country's hopes right to the bottom of the sea!