I love it!
Wow, you wasted a whole evening of mine! This is tons better than raiden X and should be very top of the portal! *ahem* normally I'm a very strict reviewer, but as here I can't be nasty I shall be constructive instead.
With the gameplay I find it very entertaining and I like the fact that there are no homing missiles for the lazys, so it always requires actually moving, and dodging bullets ect. I like the fact that your lives respawn, so that better players don't get it easier in later levels (as in raiden), and I like the fact that you ditch the "pick up powerups and get into places where you are easily shot" for "buy your weapons sensibly and switch between at will".
The graphics are nice and the shading is done well. I'm not sure if the stylish b+w is better than the clear & fun full colour, but it looks nice at the moment so I won't complain about it (I had fun messing with invert colours).
The sound is a little annoying and I favoured weapons which made almost no sounds because the weapons are pretty bad, and yet I didn't turn sound right off because there is a certain thrill that only comes with a big explosion when killing a boss. The music complimented it and didn't take over, so that was pretty good.
Style finally is awesome. I like the setup, the menus, and as said the b+w works well. I really can't say anything to add that would make a sequel better, it's spot on as it is.