Long games are good. If you really start to get into a game, then it ends, it sux. But a good way to fix that would be to make a random dungeon generator (if possible with RM2K) such as in Diablo, but more specifically like the Ancient Cave in Lufia 2 for the SNES. It was a 100 level randomly generated dungeon that had awesome replay value.

What is it they say about silence being golden?