I was in Nice in May. Unfortunately, I can't tell you much, because I wouldn't recommend our hotel we stayed in (I think it was a Clarion hotel?)
Enjoyed walking around. We took public transportation everywhere, it cost us only like 1 euro each to get to Monte Carlo by bus. But for some reason from the airport it was 4 euro each, a much shorter journey. Picked a random group tour to go on-One of those all day things. We enjoyed it, candy factories, beaches, etc.
Have fun! I imagine it will be roasting hot this time of year, since it was scortching in May.