"Muy simpático" is very nice as in kind, caring. "Muy bien" is very nice as in very good.
(Tú) eres/usted es muy agradable (informal/formal)
Son / sois muy agradables.
He was very nice (he is a very nice person, always) - Era muy agradable He was very nice (he behaved very pleasantly) - Fue muy agradable
Son muy amables means "They are very nice" in Spanish.
"She was a nice person" in spanish is "ella era una persona amable".
You would say "una persona muy agradable".
You could say "Mi madre es muy simpático."
It depends on how "nice eye" is intended. If you are referring to the expression indicating that a person is very perceptive and notices minor details, the expression in Spanish is "De buen ojo" If you are merely trying to say that an eye has a nice shape or that it's pretty, you can say "ojo lindo".
Mi mejor amigo (a) es muy agradable.
agradable !
burrito
If you'd like to tell someone to cheer up in Spanish you would say alegrarse. This is a very nice way to brighten someone's day.
Soy simpático(a)
¿Ha sido agradable a tu hermana? is the best way to say "Have you been nice to your sister?" in Spanish.