The game is great, great replayability for me.
Don't know why you had to cheat to beat the last mission, it is just a straighfoward push in the lions den and leave alive.
There is a way to beat it without cheating, you just have to know the route to take, and move fast less the Russians will fortify it by the time you get there and they fortify fast. Sure they may outnumber you and keep dropping seemingly unlimited reinforcements but hey that is what makes it fun.
By the way I play on the most difficult level every time, the last time I played this game I beat that mission losing only 5 heavy tanks. (which I lost assaulting the "fort")
Tip: Give your army a repair vehicle or two and keep them out of harms way and they will keep your tanks alive and firing while the Russians die in front of you.
And ignore the destroyers, attempting that side mission will just divert your men and resources and end up costing you more than you bargained for. The destroyers do little damage anyways once you get deep into the heart of Seattle.