my husband and i both read this and he first said "that halo game can be addicting".
the first step may be trying to become close to your husband again by spending alone time with him(i know you are busy but this is important) and listening to him,he may be having hard times with something you do not know about, and then when you feel a little more connected you can present him with your advice on his parenting. you are right in being upset at his distance towards the children but it is always difficult hearing about what you are doing wrong, so be gentle with him.
another suggestion to get him involved without him feeling he is being repramanded is try a family night where everyone does something together, games or an outing. no one can opt out. if your husband has a hard time being alone with the children on sat mornings write a list. they can be clueless as to what the kids need to eat or chores to do. my husband hates chores but he loves my list(always with a "thanks, i love you" at the end) because it lets him know what is expected of him and he knows he will get praised when i come home and he has done everything.
good luck and remember to be kind to him, men are fragile.