I have mixed feelings about many of the C&C games.
C&C - Good fun, but painfully hard at times.
Red Alert - Some of my best gaming memories are playing skirmishes on this with a friend via null modem/com cable. The campaign was also nicely balanced apart from the indoor missions.
Tiberian Sun - Fun story, fun units and enjoyable gameplay. I've never really understood the hate this game gets as its one of my favourites. Also, James Earl Jones!
RA2 - Probably the best game of the series. The campaign was great fun and some of the units were great fun.
Generals - I will admit I never really gave this game a chance as I switched it on, saw they changed the build scheme to be more like other startagy games, went WTF is this shit? and un-installed.
C&C3 - Again, I could never see why this got the hate it did. The story was a good continuation of what came before and the units fun to use.
RA3 - Previous games were camp, but played straight. In this they went too far the other way which got annoying after a while. Also, the fact you were forced to play in pseudo co-op with the AI really annoyed me.
C&C4 - I played one mission before giving up. Using the last game of a beloved series to try and shake things up is a REALLY STUPID IDEA!