People really find WC3 harder than 2? 3 is one of the easiest IMHO. 4 is hellish, 2 is pretty hard, 1's got its heavy duty moments (mainly in the add-ons)...
But 3 and P are fairly easy. SO can be a tad hard too.
Nevertheless I believe WC to be one of the less punishing series in the Space-Sim "market". X-Wing, Freespace and I-War are all harder to play. I like the WC way better. Even if because in mosto fo the games, if you fail one mission you can go another way, try an alternate path. It's a lot more imersive.