I'm the opposite on this. The more walls to take damage of, the bigger hitbox, the worse shooter for me. I also like everything about Cave-games except chaining (and as Joe said, the music sucks. But I think most of the video game music sucks) - one of the last thing that makes them interesting to some players. But I just want the core, the "avoid bullets and shoot".
Oh, and the biggest dealbreaker for me in shoot 'em ups - is horizontal. I have to this day not liked a single horizontal shoot 'em up I have ever tried, and I have tried a lot of the popular ones (Border Down, Deathsmiles, R-Type-series, Gradius-series, Einhänder, Darius-series, U.N. Squadron, Thunder Force-series, Progear etc). It's vertical all the way for me.
But I still love the shooters on PCE for some reason, that was even the primary reason for getting a PC Engine in the first place.