I played this game for about an hour and 1/2 and it's really fun!
I had no idea that the main gun was a machine gun, it's so cool and it reminds me of Operation Wolf, one of my favorites at the arcade when I was a kid.
Good solid action, and a pounding soundtrack and excellent controls make this one a must have on my book.
The aiming is pretty good too, It's actually easier then the arcade because you have a cursor on screen and it's easy to score head shots.
But you can also calibrate the Wii remote and disable the cursor for an authentic arcade feel, and it works surprisingly well, really, although I suspect that with the zapper it's even better.
All in all I'm loving it, especially since lately I haven't been able to play house of the dead 2 for my Dreamcast because of my new lcd HDTV.