How is Nergal a boring villain? He loved a dragon during the Scourge and helped his children (Nina en Nils) escape through the Dragons Gate (see chapter 16XX), telling them he would get back to them. But the stronger you become in black magic the more of your personality gets destroyed (look at the guy from the eight heroes he has no personality left). So over time he only remembered he needed power, and wanted to open the Dragon's Gate. But he doesn't remember Nills an Ninian as his children anymore,only that he wants power although he doesn't know for what. Actually really tragic!

I found it one of the best endings, and I'm far from alone in that regard. But i know people are in two big camps on it. So a divisive ending instead a bad ending i guess.