A lot of you are probably gonna call me crazy, but I actually like C&C3, RA3 and their expansions...They're not that bad.
C&C3 is a lot more basic, but actually fairly well balanced. RA3 initially had quite a lot of issues, but it's expansion added units that solved almost all of it's balance problems. Such as the Empire not having a low-tier Anti-Air Infantry...
In fact, in RA3 Infantry are ALMOST a viable composition, especially for Soviets.
C&C4 I do not like, it looks horrible and just down-right bad concept. It's like they wanted to turn C&C into a MOBA (Wtf? That's entirely the opposite of what C&C is about). Yet surprisingly, it has a pretty large competitive scene, in fact there's even a fairly popular channel on YouTube (That I'm even subbed to) that shows almost entirely C&C3 and C&C4 high-tier-player games.
Functionality-wise, concept-wise, capability-wise, Red Alert 2 (With ARES expansion DLL) is probably the most promising C&C game there is to date. It's got tons upon tons upon tons of mechanics that make the game really worth modding and trying to make something good...Although base RA2 (And YR) are not that great and not very balanced at all.
What makes a good RTS good is balance, variety, and skill-based concepts such as tactics and micro.
RA2 has tactics. It's balance is very loose, but only because of it's concept. If it's economy and production was a little bit different, it would be woefully more balanced. But it still has variety issues. In fact, all C&C games suffer from variety. Vehicles almost entirely have all the power and nothing else can stop them but vehicles.
Not even Infantry, or even air units, that are designed to take down vehicles, can be produced as quickly or in enough quantity, and in the Infantries case they just straight up don't have enough power, in order to take down a vehicle-based composition.
But after all of this, we still have an Open-Source project being developed by some very talented people called OpenRA. It's quickly becoming much more promising then RA2, with them working on an Isometric terrain system, Voxel support, and making many other things such as mechanics from RA2 like Mind Control, Magnetron, and Marriage Tanks.
OpenRA will replace RA2, it will only take time.