RA3 was too much on the wacky side for me. I've played a few skirmish games and 5 Soviet levels, but I couldn't really get myself to go further. I understand that RA2 was also wacky fun, and it was my favourite C&C RTS gameplay-wise, but the weirdest it got was just things like desolaters, chronosphere, iron curtain, IFVs, etc. It all seemed at least plausible. In RA3 however, I couldn't really care for the sailor moon/girl scout units and Gundams. I can see myself trying it out again in the future, but my preference for a game is that it must at least be believable in some way. Not necessarily realistic, but believable.
Generals offered nothing special to the RTS genre; it was basically a Warcraft-type game set up in a "modern warfare" direction. Multiplayer just consisted of guys building a dozen bases all over the map and unit spamming the enemy. Singleplayer was way too simplistic and boring; long missions that are neither challenging or fun, no storyline at all, no cutscenes, etc. I hated the mere cheesiness of the GLA and China. Zero Hour introduced a few characters, but didn't expand on them at all.
C&C3 was pretty good, I liked it, besides the plot holes and disconnections from TS. The storyline was a bit dry; I don't think Nod was portrayed in the correct way, and I'm not a big fan of alien invasions - it's been overdone in movies and games. Tiberian Sun's vines, underground units, exploding tiberium, Tiberium plants/fauna, and the Forgotten all just disappeared. The tech was backtracked: from Mechs to tanks, from Cluster Missiles to Nukes, from Disks to grenades, from super units to unit spams, from amphibious APCs to normal ones, etc. I liked C&C3s gameplay a lot, but it felt a lot more like a sequel to C&C95 than TS. I'm not saying that's a bad thing, but I would've preferred Westwood's "Tiberian Twilight" over C&C3.
C&C4 was just a disaster on all ends.