I've had it recreational only meaning never from a dentist, currently have a dispenser and use cartriges when I do use it.
On its own, if its cheap its okay but honestly nothing special considering its shorter lasting than crack cocaine, even shorter than a cigaretter buzz. The most noticable effect is the auditory effects, meaning one you've had it everything goes to an EXTREMILY high pitch for example someone talking can sound almost child like mixed through the constant buzz buzz going around, this goes on prob as long as you have it in you.
Now I never liked ketamine, I actually liked DXM better than K (different strokes) but the BEST thing you can do with n2o is have a bump of ketamine (i assume dxm would work too since it too is dissociative and has k like effects however dont recomand this since dxm is 6-8hr while a bump of ketamine is max 1-2hrs).
I've had my most intense psychedelic experience after a bump of ketamine and a buddy filling up baloons (up there with DMT except extremily euphoric and completley different)
Conclusion: n2o is best used with a psychedelic or dissocicative, however i've used it on almost anything including opioids and it makes the high a bit better.
p.s. havent tried it but i heard its amazing on MDMA, id try some on the plateau and one on the comedown