I have always been especially intrigued by how Elvish seems intrinsically beautiful, while Orcish is ugly.Why is this so?
Having once pursued a minor in linguistics, I'm aware of the study of phonaesthetics that explores this phenomenon. Elvish uses lots of diphthongs and mid-vowels (e and o) whereas Orcish has no diphthongs and is confined to the primary vowels (a, i, u). Elvish also uses velar stops (k, g) infrequently and, as far as I recall, does not use any velar fricatives (kh, gh). Velar sounds prevail in Orcish. Orcish also allows abrupt consonantal clusters such as we hear in words like "nazg" and "Lugburz" whereas almost all consonant clusters in Elvish involve the so-called liquid consonants l and r.
You can hear how all this affects you phychologically just by comparing the Elvish "Ai laurië lantar lassi surinen" to Orcish "Ash nazg thrakatuluk." The Elvish sentence sounds like water flowing over stones, while the Orcish sentence sounds like you're trying to cough up phlegm.
Similar sorts of phonaesthetic "rules" explain why most humans find the Romance languages (French, Portuguese, Italian, Spanish) to be "prettier" than Teutonic languages like German, Dutch or English.