C.K.
L. your husband is out of line and out of control. His gaming shouldn't be coming between him and his family.
A year before I had my three kids I was a 4-8 hour a day gamer. Immediately when I can home from work and huge chunks of the weekend were devoted to my game. My wife was really upset by this and it took us some time to set up a system that worked for the both of us.
I don't know the intricacies of your marriage, but I realized that my marriage was much more important that any game I was playing. If I had to leave the game no one REALLY died, the world didn't REALLY end, and that next LEVEL was still going to be there for me when I could get back. He needs to come to this same conclusion, especially if he is ignoring his children as a result.
My advice for you is to really think about what you want and what you think fair requests to make to him. Write them down. Then do the same thing from his point of view. This will give you a chance to reflect on the situation before you confront him about it.
Next, find some time without the kids and talk to him. It might mean staying up until he is done gaming for the night, but this is important enough to warrant this. Once you have his attention, calmly state (or restate) what is bothering you and what you want. Then tell him exactly what you think is acceptable behavior from him (meaning how much he plays and when). Try and be as non-threatening and understanding as possible, even sympathetic to his position if you can.
Now, if he refuses to budge on his behavior or starts a fight, then I think the two of you would be good candidates for some counseling and you need to tell him that. He needs to understand that his behaviors can ruin your marriage and unless he wants that to happen, then he needs to make some changes.
Good luck. If you think it would help him to hear my perspective, you can share my letter or have him contact me and I will be very honest with him.