I'd have to echo the statements that say it is worth it. I like the new features and even the handful of new ships they included. Even though I had my fill of U-Boats in the Atlantic with SH3, the Indian Ocean with the new U-Boats is interesting. The Type IX is my favorite U-Boat, but I never used it in SH3 because of the long patrols and painfully slow 1024x TC. It's nice to finally be able to use the Type IX. My only continuing gripe with the add-on is the absence of German speech/sound files. I know there is a mod that changes the speech and sounds to fit the U-Boat side of things but it takes so long to enable in JSGME and since I like to switch between sides rather frequently it just doesn't work to well enabling/disabling the sound files all the time. I just don't know why they couldn't have included the sound files and told the game to load English for the American side and German for the U-Boat side (like they did for metric/imperial measurements). Even the trailer they released before releasing the add-on used SH3's German speech and sounds.
