I played through the entire game in 2004 (the original, not Third Reich.) The ending works pretty well emotionally. There were a few levels that almost got me to quit, though, particularly the underground/ant levels.

I played through the whole original Freedom Force when it was originally released. Loved it. Didn't go for the "Third Reich" expansion because I was not super interested in more WW2 sounding stuff at that point and as a youth my gaming budget was quite restrained.