I'm not a big fan of Namco in general, but I did enjoy Valkyrie no Densetsu quite a bit! It's the closest thing to Etoile Princesse that I know on the PC engine, even if it's not quite as good as that, but it's still pretty fun! Good music too, also, gotta love those scaling sprites ;3
My other two picks were Samurai Ghost and Bravoman, which I tend to think of as guilty pleasures, but what probably does it for me in them is the parallax scrolling, I mean seriously those games tried SO hard to do parallax I can't help but respect it! And it doesn't look THAT bad right? I mean, at least Samurai Ghost is better than Ernest Evans...
Also, I know Splatterhouse is a classic and all, but it just didn't quite do it for me... Sorry ^^';