Diablo where you control a large party -- I tried this idea myself (using a bit of hack) and found it to be such great fun and extremely addictive. The only bad thing about it is that you can't go back to a single-player Diablo any more :-) There is a webpage that I made about 15 years ago: http://pl.postech.ac.kr/~gla/diablo.html

I still play Diablo with 8 characters occasionally. I wish there was a game like this.