Here are some possible ways to express a similar sentiment in French, depending on the context:
If you mean "You are amazing/awesome":
* Tu es génial(e)! (You are awesome!)
* Tu es super ! (You are great!)
* Tu es incroyable ! (You are incredible!)
* Tu es le/la meilleur(e) ! (You are the best!)
If you mean "You are really cool":
* Tu es vraiment cool ! (You are really cool!)
* Tu es trop cool ! (You are super cool!)
* Tu es un(e) canon ! (You are a hotshot!)
If you mean "You are something special":
* Tu es unique ! (You are unique!)
* Tu es quelqu'un de spécial ! (You are someone special!)
Remember to choose the phrase that best suits the situation and your relationship with the person you're speaking to.