"The hat is great!"
Translation:Der Hut ist toll!
Colloquially, people might say something like, "Wow, where did you get that hat? Der ist ja genial!", meaning "awesome". But personally I wouldn't accept it as a translation and I'd suggest to stick with "toll".
Normally "genial" = "ingenious", e.g. an invention, or using a tent as a sandbox (so the sand stays clean and the tent protects the child from the sun).
Your native pronunciation of English will affect the comparison, but if I am correct in assuming you're North American, the closest pronunciation is ‘aw’ (as in ‘claw’). If you're familiar with RP, then the closest ist the ‘o’ in ‘boss’ (but US English has a more open and less rounded pronunciation of that, so it wouldn't work). Anyway, the pronunciation isn't really different from any other German word with a short o.
German doesn't really have a vowel that similar to ‘uh’ (at least as far as the most common standard pronunciations of English go), the closest possibly being unstressed ‘e’ (like in ‘Straße’) or ‘(e)r’ (like in ‘Butter’).