Its difficult to describe.
There is no ouch because naturally, its not just laughing gas your also frozen up so much you can feel your face. What the gas does is make you feel so giddy and light headed that you don't have a care in the worl and in dact, find it totally fucking awesome that your biggest molar just got splintered into three pieces by an inductrial size clamp and removed section by section from your gums.
You don't feel the pain because of the extensive freezing. It just takes away the feeling of revulsion.
If I were to make a suggestion I'd say absolutly go gas. Its a blast. I had fun getting my wisdom teeth out. It was only after the freezing wore off at home that it sucked.