她/他 人很好。

酷 usually is the frequently used phrase to describe "cool" in Mandarin, and I guess you can use when you want to say awesome. BTW, you can also use 赞 which is not so often used as 酷

There's a very fashionable word that can describes it. 拉风。So you could say 他/她很拉风. Personally, I really like it

他／她很棒！

他/她很厉害/太厉害了！。