Almost every port form the 16bit era could have been better in terms of BG details etc. IF you had some more memory available. The cd-rom had proven that quite well.
Considering that, most Arcade to PCE ports were done quite well, and sometimes they came very close to an arcade perfect translation.
I think this is my problem - I look at what happened with Ghouls and Ghosts, and yes, I know it's a Super Grafx game, but everything is so... right.
But I'm sure the PCE could have done better.
And I would like to add, that I kept playing it after I posted this topic, and I was quite impressed by the variation. I got to level 4, with the mirror images, and the cross surrounded by floating heads. Whatever criticism you aim at the game, it's hardly unimaginative.
I'll certainly be playing it again. Time will tell.