Hello,
I've tried last Saturday night Snowball and everybody liked it, so I 'm gonna start a campaign in Middle Earth with Snowball.

I have one question. Do you create a new character in every session or do you keep the same one with the same traits and with the right to create and new traits?
How do you play your games?

I don't know if it is right to allow my players to keep the same character, because they may become at the end, after many sessions,  super heroes with so many traits and with the right to give them more dice in every scene.Please tell me what do you think about this?

It's totally okay to allow players to keep their characters through multiple sessions.  They won't become superheroes, necessarily, they'll just have a whole bunch of traits, as characters in stories tend to do over time.  That said, Snowball was designed with the short story in mind, not necessarily a long campaign.  Nonetheless, since each new trait or trait level has to be paid for by dice, and each level is more expensive than the last, there should be a natural slowing, unless they decide to create a whole lot of one-die traits (which are limited in their usefulness).

Remember, every victory means a loss of all gambled dice. 

Anyway.  I totally think it's right to allow them to keep the same character.  I'd be very interested to hear how longer-term Snowball play goes, though.