Simple question really: should the final boss of a game be difficult (relative to the rest of the game)? It's hard to say for sure, I think. On the one hand, it might not be a good idea to have the last boss be the most frustrating part of the game, since it might cause the entire game to leave a bad taste in your mouth when you're done. But on the other hand, just having it be a pushover might take a little impact out of it all. To me, Kingdom Hearts II handled this the best. The final boss wasn't exactly hard, but it was a long, multi-phase, really cool and climactic battle. Then, they had another boss which was extremely hard, but it was an optional fight you could do at any time once you pass a certain point. The difficulty of the final boss could also serve a story purpose too. In Dark Souls, for example, the final boss is one of the easiest in the game which made a bit of sense considering that the final boss was also a very old man.