An average game, for me, lasts maybe five minutes - up to half hours if I manage to beat the game. I'd qualify it a coffeebreak game all right.
Really? My wins always take upwards of 2 hours.
It's certainly a coffeebreak game compared to...well, pretty much every non-Kornel Roguelike in existance. I mean, the average first ascention on NetHack is something like 25 hours, and other titles like Angband take much, much longer than that.
However, I definitely see where you're coming from. You should try checking out Berserk!, that game is VERY fast-paced and short. It makes DoomRL seem like...something that takes a large amount of time.
I generally play Berserk! when I just want to kill 5 or 10 minutes between classes or whatever, and DoomRL when I can dedicate at least half an hour to it.