Nowadays, if I even BLINK, I curse myself endlessly when I get off. My eyes better be STREAMING or I failed that ride and, le sigh, must simply go again. ^_^
Eyes open = good.
Eyes closed = boooo.
Recently I went to Europa Park over in Germany and they have an Ok coaster with some awesome airtime and a few good drops. I decided that this time I would lift my hands and feet, and close my eyes through the whole ride.
I found what some of you found... closing my eyes took most (all) of the thrill away from an otherwise great ride! You could not tell how high you were... how far you were falling... sure it was surprising to turn into a sharp bank... but when you cannot brace for them they end up hurting your neck more than anything else.
It is a bit scarier to keep your eyes open... but closing them robs you of any thrill you might have otherwise felt.