Ok I admit, I used GOD mode to finish the last level.
I played this game on Lieutenant difficulty level (3rd level out of 4) and I was able to play through the game without much trouble up until the end boss. As the end boss is pretty tough, I switched to GOD mode, which normally I don't do in a game, but I just couldn't put myself to the task anymore. I just wanted to be done with it. And that basically sums up how I feel about this game. Entertaining, but nothing special. In fact I started getting a little bored at the end.
The game is not to difficult, where the vehicle missions are even extremely easy. In the latter part of the game it becomes slightly more challenging though, with bigger Strogg that deal more damage and are harder to kill.
I can't quite remember, but I think I had more fun with Quake and Quake 2. Then again, these games made quite an impact on the gaming community at the time and Quake 4 simply doesn't. I did enjoy it, but I was glad when it was over.
8 out of 10