"Bottom of the Sea" is as suggested by the name a naval affair. It takes place nearby a coast; this is all we are really told about the story.
Playability: The playability was not so good, the missions seemed dull and un-interesting and failed to grab me as a player. I think that constantly fighting by sea with the same units becomes boring after a given time.
Balance: The balance was a better point of the campaign, despite fighting the same units throughout both scenarios of the campaign I ended up with very few units left by the end. The balance was improved from you're last campaign : -).
Creativity: The Bottom of the Sea was not so creative. It lacked ideas, not just original ideas any at all! All enemy "garrisons" were basically comprising of the same things a few units and a small piece of land with a tower. This didn't keep the player interested although the campaign did not take long to complete.
Map Design: The map design could do with much improvement. The sea was just one type of water, namely water shallow. This was more than a little off putting as you travel towards you're enemy across the ocean you want to see changing scenery. This doesn't happen and the map soon becomes predictable. To improve it mix the different sea types, maybe add some small islands perhaps even inhabited with optional objectives to add to both the map design, creativity and playability.
Story/Instructions: Sadly, the story wasn't well thought out. The enemy still hadn't been named so every time I played it was against different enemies. The story was not really there although the second scenario was to slow down the enemy's raids but not much detail was given here, I was left guessing. The instructions were easy enough to follow but had no real meaning, as the story was not up to par.
Overall: This campaign soon became predictable and this lowered several areas of the campaign, unfortunately. Another note to the author, try using the Campaign Editor to add both scenarios together into one file this will take us less of a download time as a result, note I'm not saying the file was big quite the contrary. All together is easier to access for the downloader.