From what I understand - (and to me it's a very sad thing and makes me angry because in my opinion they are WRONG) - is that many teachers....not just art teachers....their stance/opinion = "anime/manga is not art" and they hate it or (obviously) just don't understand it , ect.

Anime is "just" the animated version of a manga series. Unfortunately many people still seem to be fixated on the idea that "cartoons" (animated features) and "comics" are "just for kids" ...same for games which is why some people refuse to believe that games can be art. (that's not true either....take Ico or Okami or the opening animated sequences to various anime/manga style games for example.)

Some really cute games with nice graphics -
Orisinal : Morning Sunshine

Although an older game, I consider secret of mana / secret of mana 2 to have some really lovely graphics especially in the flying dragon (?) friend that turns against you in the end

Although not what I'd call beautiful...Silent Hill series has some amazing visuals if you like creepy run-down looking places and nightmare fuel body horror creatures.....there's another survival horror game while the rest isn't really anything special but in that game you start out in a dreamlike place and there's two blonde twin boys dressed as angels there - I consider that pretty artsy

I'm sure there's a lot more games out there that I'm forgetting the titles of or I can't describe them - there's some really neat stuff out there that you'd have to see for yourself.....

Good question!
For me, just about everything and anything that is beautiful or enjoyable is art.
Or anything that really makes you think or gets a certain emotion (or several emotions) from you.
But even then.....not all things are art.
And I agree with the other person who stated that art is subjective - everyone has different opinions on what is or isn't art, ect. blah blah blah (heh)