Hello. Guay is slang for cool. Also "molón". A few more there must be, no doubt. I myself can relish imagining some bilingual Rastaman cosmonaut -joint in hand- overlooking Jamaica from a satellite saying: "Tío, qué planeta tan guay" (Yo Bro, cool planet). If you can too, that's your word. If you want it less slangy you may try: Maravilloso (wonderful), fantástico (fantastic), etceeeeeeetera. Good vibrations to you, cheers :)