Bubble Tanks 2
Bubble Tanks 2 is a sequel to Bubble Tanks (review here), in case the name didn't tip you off. The gameplay is nearly identical to its predecessor -- it's a pretty straightforward shooter (keyboard moves, mouse shoots) where you move from bubble to bubble defeating enemies and picking up their bubbles to add to your own tank to make it more powerful. Being hit, on the other hand, will cause you to lose bubbles.
As far as I can tell, Bubble Tanks 2 adds three features to the original. First, there's a map, which is quite convenient for telling where the heck you're going. Second, there's one huge overall boss (which is quite an epic battle), and then also four fairly powerful subbosses, which appear randomly from time to time, so that occasionally you'll get a pretty severe challenge (especially if you're just starting out; it seems like they can appear anywhere, although the boss doesn't seem to pop up until you've already upgraded your tank a fair amount). Also, the enemy bubble menagerie has been expanded somewhat, as there are now minelayers and enemy bullets which slow you, but they're still all basically built along the same lines. Third, instead of your tank just randomly gradually getting more powerful as you collect bubbles, you have a bubble progress bar at the bottom, and when it fills up, you can choose the next form for your tank. Generally you get two or three choices, each with its own advantages and disadvantages. This is a nice feature and adds a tangible feeling of accomplishment to your bubble conquest. Unfortunately, once you've chosen, you can never change your mind -- even if you lose enough bubbles to knock you back to your previous level, you still go back to the form you chose the first time around the next time you level up again. This is kind of a disappointment -- if you choose an upgrade and decide you don't like it, the only way to change is to restart the whole game.
The background music is is still very peaceful and unintrusive, and the sounds are still pretty basic. The graphics are just bubbles, though clearly whoever drew the tank models was having a lot of fun, since there's a lot of creativity in the tank designs -- as a practical matter, it doesn't affect the game much, though. Overall, this is a little more substantial than its predecessor, and it's fun to play for a little while, but I still feel like it's lacking a bit in the way of goals to encourage you to keep playing for longer.