Wow, very solid shoot-em-up here! Definitely felt like it had all the core essentials and then some: good variety of enemies, a great boss lineup with some sweet patterns to them, coop mode, and a whole bunch of satisfying audio/visual effects that really punched the combat up (love the explosions and some of the more complex effects like the croc boss beam). Game has some fascinating touches to it as well: where most games would just fade to black when you die and insta-put you back at the checkpoint, the way the game rewound the level was a cool look. Definitely was a short and sweet trip that felt professionally done: felt like I was playing Contra or Metal Slug or any other neato shooter.
I think the only demerits I can put against this game is that I don't quite agree with some of its old school design (hate losing power-ups from just getting hit once and not restoring health at a boss fight which forces you to just commit suicide to get full health lest you start at a disadvantage, but I understand its in service of the high score challenge) and that I wish it had a bit more of a sense of progress by updating the background or music whenever you beat a boss (doesn't have to be anything major, something as simple as changing the color of the background would be nice).