Yes, the game is rock-stable.
Been playing since day 1. So, yes, you can start playing it now.
People are making tons of money from RMAH. Both people & bots camp at RMAH. So, i think it's good.

P/S People can't sleep without D3 every Tuesday night (scheduled maintenance). They curse Blizz every week (since Jay Wilson can be made scapegoat no more).

P/S I heard some people got divorced due to long hours on D3. Wives are not happy when the hubbies spend too much money on gears. That's how influential it is.