soop, I'm an old-skool shoot-em-up junkie so I am not the most objective person when it comes to games like St. Dragon.
So, here are my thoughts:
(1) When I first got it, I had just played some divine PCE games (Gradius II, for example). I loved Gradius II and St. Dragon seemed like mediocre sludge.
(2) Later, when I realized that I really hadn't given St. Dragon a fair shake, I tried it again.
(3) St. Dragon is mediocre sludge, but, as you pointed out, it certainly has some interesting (albeit minor) aspects to help elevate it *slightly* above its generic brethren.
(a) I found it fun to pilot such a huge sprite. I can't recall how big/small the hitbox actually is, but it
felt different. Some folks won't be impressed, but I appreciated it.
(b) Power-up system... pretty basic, from what I recall, but certainly adequate. I don't need fancy power-up options, so you may feel differently. Give me a pea-shooter and I'm happy.
(c) Graphics/FX/character designs... nothing to get excited about. Some of the character designs are interesting, and certainly no worse than the mass-produced tin cans found in countless of shoot-em-ups. Now that I think about it, the setting and theme help keep this a tad more interesting.
(d) The action isn't balls-out furious, but the pacing was fine for me. I didn't mind it. There are many games that have boring stretches...I don't recall feeling that St. Dragon's stages were long, padded, drawn out.
I should probably play it again (it's been a while) to give a fresh perspective, but I'm too busy with Mega Zone (Konami) at the moment.