http://bombermine.ru/
That's beta version. Game is free.
Sorry, its on russian and requires small ping. Google Chrome is recommended.

Instructions: type a nickname, then press big button.
Keys: WSAD, K for bombs, L for detonation, P for full-screen.

International servers will open soon.
There were 450 players max, but i think that server can handle 1000.

Old video: http://www.youtube.com/watch?v=NnX1sin1XqE&feature=plcp

Screenshot: