No. The word nicer is a comparative form of the adjective nice. The adverb is nicely and the comparative would be "more nicely." (*The term "play nice" is just a colloquial form; play nicely is correct.)
Nicer
nicer
Sharper is the comparative form of the word sharp.
The comparative form of the word 'fast' is 'faster'.
nicer
The comparative form of longest is longer.
nicer, nicest
smoother is comparative of word smooth.
nicer, nicest
Smoothest is the superlative form of the word smooth. The comparative form is smoother.
The comparative form of the word "ugly" is "uglier," and the superlative form is "ugliest."