It sounds fine. I would use it myself.
If I were talking to, say, teenagers I might use the simpler and more ordinary word "hero."
I agree with Ceej but I would put a slightly different spin on it: the protagonist is the character you identify with and cheer for--you want the protagonist to succeed.
How about that? I just looked it up in ahdictionary and the original literal meaning, the "prot-" part, is "in Greek drama, the FIRST character to engage in dialogue with the chorus."