You can still use tickets, and I don't think they have changed in three years, couldn't swear on it though, so it's worth bringing them. If they are out of date you might be able to exchange them anyway. Regular travellers use a "Pass Navigo" which is a plastified magnetic card you just hold against the machine to open the barrier and recharge as required but you can still buy individual tickets or packets of ten, which work out cheaper per ticket.
In reply to yorkshireman: As Bruce said, they are still valid. I have some for emergencies - eg if I loose my Pass Navigo & also to get to/from CDG as the airport is in zone 5 or 6 & my pass only valid for zones 1-4