Why is it that movies over 3hours feel long...

Because they're 3 hours long. If the films is very good then 3 hours long won't feel like it, but your body will still remind you that sitting around for 3 hours is going to be tiring.

I think it really depends how interesting the game is to you. Despite being long, if the game is interesting all the way through, and the fact that every game requires your attention, time could go by quickly.

I'd say it's probably because when you play a game, you're interacting with it. You're keeping your body occupies by controlling what's happening. It sucks you into that world and time just passes by.

When you're watching a movie, you're sitting there, watching people on the screen do things.

I played Morrowind GOTY for hours on end and didn't WANT to go to sleep but, eventually I did fall asleep. I enjoyed watching Titanic and didn't get too tired. Maybe it depends on the mood your in I guess.

Depends on the movie really but to me movies that are 3 hours feel long because you've been sitting on your butt for 3 long hours staring at a big screen. With video games, I rarely spend more than 3 hours at a time. Normally I spend 1 or 2 hours on them.

Your mind is more active playing video games. In movies you just sit and watch.