You are too fast.
So far, I found only three online games that suit my tastes:
- Kingdom of Loathing. Distant relative of the old MUD "Legend of the Red Dragon". Gameplay is quite simplified: you have limited amount of turns per day, and your global task is to kill the Big Boss, ascend and get more skills and items, rinse and repeat.
Plus side there is the community, sheer amount of content and good writing.
- Gems of War. Simple match-3 battle in vein of old good Puzzle Quest (and from the same authors), only without plot, but with infinite amount of different units.
Nothing too much, but it can be played for free (really free, I mean, it's not required to pay for progress), and have enough mechanics to allow my brain juice ticking - and quite fast to play, so I can spent 15-20 minutes per session.
- Path of Exile. The best that happened with Diablo-like games from the times of Diablo 2 (and much, much better than D2).
Can be played _almost_ free. If you will never buy the extra inventory tabs, endgame gameplay became quite cluttered with all this good items that haven't any place to put into. Refreshes each "season" (roughly half-year) with new mechanics and items.
Everything else I seen either too expensive, or looks free - until you hit soft wall of infinite time for progress.