Escape from Zombie Island 2.
So much fun to play. 15/10 would recommend.
Man, I'm still amazed how they overcame Civ3's lack of scriptable events. Been digging through it for inspiration ever since.
For C&C Generals Zero Hour:
ShockWave
What always got me about ZH was how the faction generals only changed one or two features, some for the worse. ShockWave overhauls their entire arsenals, making each a unique faction in one's own right. The mod is compatible with the campaigns (or at least seems so), and the Generals' Challenge has been expanded to cover all leaders, including the two unimplemented bosses. The only major complaint I've heard balance-wise is that artillery is generally OP.
Tiberian Dawn Redux
The original
Command & Conquer in the SAGE Engine, re-implementing the construction yard system (although t'would be nice to see build ranges), and including the original campaign missions! A previous version even had the briefing videos which for some reason were cut in 1.4. Features widely expanded graphics that give it the shine of C&C3. It's been inactive for four years but the current build is stable.
Cold War Crisis
I don't think I've ever encountered a total conversion mod that lives up to the adjective as this does. CWC basically turns Generals into an RTS version of
Operation Flashpoint. Units and buildings are ridiculously detailed and weapons are modelled realistically, meaning a handful of well-placed rocket troops can take out an Abrams tank. and the in-game AI has been recoded to something like a factor of 10. Now, this comes with a pretty hefty qualifier: gameplay is closer to RTT than RTS and approaches CoH-levels of micromanagement, without the benefit of an in-game pause key; aside from the engine it is an almost entirely different experience to Generals. Nonetheless, read on its own merits it's one of the most ambitious and polished packages I've ever come across.
Eastern Front for CoH1
All the fun of the Red Army, none of the political bull. And unlike CoH2, it's free and fully compatible with the original factions.
For Red Alert 2: Yuri's Revenge:
CannisRules (requires
Terrain Expansion Pact)
A scope-simple but effective mod that adds new national units and gamemodes and rebalances the factions; I believe it's also compatible with the campaigns. After getting it I simply stopped playing the vanilla. The original site (which gave detailed info on the mod) is now dead, but it's straightforward enough that you don't need to re-learn the whole game.
Mental Omega
Billing itself as "Almost Perfect Yuri's Revenge", it also started out as a balancing mod but expanded into what amounts to the ShockWave treatment for YR, diversifying the existing factions and giving Yuri two new cells of his own. Version 3 introduces new campaign lines for all
three sides that are considerably more challenging than the original.