Wave 12 was stupid as shit and time consuming with extremely little space to move around in.
As for basic gameplay......Average with some problems. Moving around things was a pain in the ass, and shooting was even more of a pain in the ass, because even if your mouse button is still your ship is slowly moving forward, making it a pain in the ass to actually shoot something without ramming it.
The upgrades did too much. By this I mean; If You get hit once on a hard wave, or maybe even more, You pretty much forfiet your ability to complete that wave.
One of the most fun things I do in this kind of game, is making comebacks with incomperable odds. But in this case its completely out of the zone to even be able to do shit later on without your upgrades, so I quit almost immediately after I realised this.