I'm more of a casual player when it comes to shoot em ups, but this is easily one of the best arena shooters I've ever played! It's being developed by three former employees of SEGA Australia. It's currently in Steam early access, but the PC version's slated for release this November, so it's mostly completed. Console (Wii U, PS4) versions coming 2015.
Don't let the dumb name and crappy character designs put you off.
Tried the demo for this a while back. It played pretty well! Nice and responsive, and thing get hectic pretty quickly. The look of the characters, though...yeah, somewhat off-putting. They did grow on me after a little while, I'll say.
I think we need a 5-year moratorium on twin-stick co-op overhead arena STGs. The genre has become incredibly oversaturated with mediocre to poor quality games in the time since Geometry Wars made it popular again.