you know, if his grades are good and his behavior at school is good, your son might do better without medication. it's even possible he doesn't actually have ADD (it gets misdiagnosed a lot!). my parents tried micromanaging me when i was his age, and even then, there was no way i could ever make good grades in school! i just couldn't concentrate! adderall worked for me, but there are alternatives to medicating.......
your son could be having reactions to the chemicals in the foods he eats. artificial colors (especially red 40, yellow 5 and 6, and blue 1 i think), artificial flavors, preservatives, high fructose corn syrup.... these are all things that can cause ADD-like behaviors, or make ADD worse in a person who has ADD.
as an alternative to medicating him, you could try switching to all natural foods. most grocery stores and national superstores (target and walmart!) offer natural brands in most foods. you do have to look around for them, but they are there. read the labels on everything! even bread has high fructose corn syrup in it! fast foods are killer for ADD, and i am pretty sure school lunches are the equivalent to fast foods....
other things that can contribute to ADD-like behavior, or make ADD worse are lack of exercise and lack of sleep! make sure your son gets enough of both!
stress is a huge factor with me and my ADD. your son might be getting some highly needed stress relief when he is playing his games. i would not take them away from him completely! definitely limit his playing time, but talk with him and ask him what he thinks would be fair. set some ground rules together (like his homework and studying, chores, dinner, etc.... needs to be done first before he can play, and then he can play until such hour and then turn it off....), and be sure to listen to his point of view.
it's fairly typical for a 15 year old to be sullen, surly and disrespectful to parents who are trying so hard to micromanage him! i'm not saying you should just sit back and take it, just offering some outsider's insight on why he might be acting that way. it's something he should NOT do and definitely needs to change, but perhaps there is another way other than micromanaging him?
something you mentioned in a previous post was that your other children are so organized and he isn't.... i would strongly advise you to NOT compare him to your other kids. he's not them! he is who he is and all the micromanaging in the world isn't going to change him! if it's helping him keep his grades up, then it needs to be done with his schoolwork, but outside of schoolwork, are you still trying to micromanage him???
all this rambling.... can you tell i'm off my ADD medication (i'm pregnant so i'm without my adderall right now!)??? my point is that your son might just be a different type personality than you or your wife and your other kids and instead of trying to fix him, embrace him for his differences. learn from him. sometimes it helps to lighten up and not be so incredibly organized and disciplined. he is probably a little too far the other direction, but once he feels your acceptance of who he is, he might be more willing to find a happy medium between the two extremes.
anyway, hopefully you could find something useful in all this!