I think it very depends on the age of the person who says that. Different word with meaning awesome would say someone who is 18 than someone who is 30.
Gementrix--would uzasny! be a pretty good choice? Mimochodem, to je fantasickou otazku od tebe pred nejakem zrcadle. Zda se mi, ze je hezky specialni efekt. Snazil jsem se podobne veci, ale ne se tak dobrym vysledek.
uzasny isn't quite a good translation i think. uzasny is like amazing. the closest i can think of is husty, which is like cool
I prefer ohromující. It is ambiguous in the same way as English awesome. But maybe it is too formal. Or, maybe similar ohromný, in formal Czech it means huge but in colloquial or expressive speech it's quite fitting.
skvělé is correct because I was reading this and asked my czech step daugher "Co je skvělé" Without reading the forum, she immediately answered "awesome".