Easy, Imbalanced, Short, and overall disappointing, but OK I guess.
That's not to say the game is necessarily bad, but its easily the worst in the canon CNC games.
It seems that Red Alert 3 has two faces; there's the story and movies and then there's the gameplay. The story and movies are Dr. Jekyll. The gameplay is Mr. Hyde. The story here is hilarious and the acting/movies are just as silly and fun, my favourite character being the premier of Russia who is played by Tim Curry. TIM FREAKIN' CURRY!!! Seriously, more games need Tim Curry. It's just as cheesy, cartoony, and funky as you expect from a Red Alert game. These bits are by far the best part of the game, sad to say.
The gameplay at its heart is a traditional RTS, and its good for that if nothing else. The units are varied and the naval idea is neat and lots of fan favourites return. There's also a Generals-ish "Upgrade" system, which leads to some fun new moves. That means there is a lot of potential, but the design and balancing is just downright sloppy. Skirmishes/multiplayer matches aren't like those of any other CNC game, which are frentic games of Rock Paper Scissors where you have to use all your weaknesses and strengths to eventually hit your enemies underbelly and take them out. In Red Alert 3, it can go one of two ways: You can play as the Russians or the Allies and fight more Russians or Allies and have a good game, or you can play as the Japanese and instantly crush your enemy or you can make the mistake of fighting the Japanese and die before you can build your first power plant. The Japanese are the most imbalanced faction I've ever experienced in any RTS. Not only is every building mobile and have a 3-4 second building time, every unit has a ground mode or a flying mode, and in either mode they can attack ground units as well as air units. There is simply no way to counter the Japanese. If you prepare for an air attack, they can just go onto the ground and win. If you prepare for a ground attack, they go into the air and beat you. If you prepare for both, you'll soon realize that your defenses and units can't attack air or can't attack ground (even on the ground) and you are screwed. When you aren't faced against the Japanese or playing as them, the game can be fun. This is the one area where the gameplay actually works.
Despite that, the actual campaign is surprisingly easy. You rarely have to think and each mission lasts maybe about 5 minutes and there are only 18 missions in all. I beat this game on the hard setting in an hour and a half and never broke a sweat. In fact, I didn't even have to think. All the objectives are so easy they are solved the second you are given a briefing. The campaign is a total throw away.
On the upside, the game looks great and sounds great. The voice acting, even with the in game units, is very entertaining. Conscripts are absolutely adorable sounding, spouting out cheery and clumsy but cute and funny clips. Each unit sounds like it should, and they look great visually too. The art style may be an acquired taste, but I for one loved it. It's a surreal mix of cartooney and realistic that works surprisingly well considering the setting. Battles sound great and the music is for the most part equally good, the only time the music really hits a sour note is with the Japanese - some tracks for them are O.K. I guess, but sometimes it sounds like a cat being raped, and I know its supposed to be chanting in Japanese but it comes off as awkward, I don't know how they managed to do it, but they managed to make the Japanese language sound ugly with those tracks. The rest of the score is stellar.
In the end, RA3 is... just okay. The allies and Russians are fun to play with, but the Japanese completely break the online and skirmish components, and a terrible campaign ruins the otherwise good core gameplay. The best part of the game is its charm from the voices, videos, and graphics, but in the end the game itself could have been so much more.