i play a webbased game many years now...
They have 80k players online,it is very good and it is free...
It is called Utopia,a medieval strategy game ...
It is played in "ages" who last usually around 2-3 months,you can play whenever you want,that means that you can logon once/day or more if you want...
It is based on "provinces" and each player controls one then 25 provinces form a kingdom,the 25 provinces elect a "monarch" who leads them into wars with other kingdoms.
The game is based very much into relations between the players (that is what i like so much)
go check it at www.swirve.com
If you have any questions ask me