Summary
A step down from NAM
The Good
WWII GI is a sequel to NAM; instead of fighting in the Vietnam war, you fight in World War II, as the title suggests. My favorite thing about WWII GI is the level design - the entire game takes place in France, and WWII GI succeeds in that. You'll fight in towns taken by the Germans, and it definitely looks like it. WWII GI has lots of cool features that are pretty cool for a build game. You'll find Anti-Aircraft guns that actually shoot missiles into the air, as well as planes that fly by and drop missiles/supplies down at you. Pretty cool. There's also tanks, and while they don't move they succeed in sending a chill down your spine when you hear their grinding noises.
The Bad
WWII GI was definitely a step down from its prequel, NAM. In NAM, you could use gun-emplacements on your enemies. Not anymore. Also, the weapons are cool but lack reloading animations, except for the Thompson and MP-40 - the rest just shake around when reloading.
Also, the developers apparently didn't take a hint with NAM's difficulty - WWII GI is even worse. You now have a morale meter - whenever you are shot at or your buddies die, it decreases. The lower it is, the worse your accuracy is. While this is an interesting feature it just makes you hate the game even more.
Finally, WWII GI has very little music - as such, they repeated the same songs over and over again. You'll probably end up turning it off.
The Bottom Line
If you enjoyed NAM then you should probably get WWII GI. It has the same gameplay with a couple bad points, but you'll still have a good time with it.