I freaking love Demise. People say he didn't have characterization as a villain, but he did; all throughout the game we are told of his actions and character even though he isn't physically there. He may not have shown you much in person, but that along with what is told all throughout the game is quite sufficient; much more, in fact, than most of the villains in the franchise. Ghirahim makes constant references to reviving his master, and we fight Demise's beast form numerous times, so we know what he's capable of even at a lesser form. He commands an entire army of demons, which is said at the beginning when the demon tribe nearly wipes out the human race, and it is made quite apparent at the end when Ghirahim as the surrogate leader sends hundreds if not thousands of the Horde after you. And the presentation is quite awesome; the first time I saw Demise I was truly intimidated by him. The huge bulging muscles, the hair made of fire, and the fact that he only cares to wear a toga paints a picture of a being who knows he can kick your *** and get away with it.
And I had no problems with the fact that you could heal yourself before fighting him. Again, he knows he can kick your *** and views you as a tiny weakling, so to him it makes no difference whether you heal yourself or not. My thoughts mirror that of JuiceJ's on this matter, he's created an alternate dimension to fight in (which gives him so much credit as the most powerful evil being in existence) and beckons you to follow, not just standing there at the bottom of the spiral descent shooting the breeze.
Gameplay wise, he's the hardest boss I've fought by far. I never did learn the trick to drawing lightning into your sword, so I had to fight him using pure sword skills. No reliance on stupid cheap tricks or glitches, I had to develop new strategies on the spot while fighting him. And I died three times before I finally eked out a victory with only six hearts left. And even though I know the supposed "real" way to fight him now, out of respect for him I refuse to ever use that cheap move. And I loved the fighting arena itself as well, it wasn't just a random patch of dirt with dark, gloomy skies overhead like it's been done so much before, it's in an ALTERNATE DIMENSION, in what appears to be Salar de Uyuni, Bolivia in the rainy season!
Best final boss fight ever!