This seems to be an expansion to the base Diceland game, but I was wondering if it was playable by itself.
"Deep White Sea" is not an expansion. It was for some time even the only Diceland product available.
All of the Diceland packs are playable alone, maybe apart from the "Extra Space" Set, but even that had an army that could be split for standalone play.
Getting back to "Deep White Sea", this contains 5 ready-to-play armies and in my experience (I own all sets) it's the set with the most variation between Armies, so it's perfect if you only want one set (all sets can be mixed, even if "Dragon Shaman vs. Alien Spaceship" seems a bit odd).
Just make sure you download the updated rules from the Diceland website, there is one change made for sets following "Deep White Sea" that changes gameplay drastically (you may now move or activate a die after throwing, the old rules allowed only activating).
Hope this helps.