To sum up RA3 in one mental image, imagine David Hasselhoff playing the American President. Then the director telling him he's playing it too seriously, and needs to ham things up a bit. If that mental image amuses you then you'll get on fine with Red Alert 3.
Continuing the alternate-history theme established by Red Alert, in this installment you see Premiere Tim Curry (yes, THAT Tim Curry) hurridly uses the time machine developed by boffin stereotype Dr Zelinsky to go back to prevent the defeat of the Soviet Army, which they do. With the slight side effect of a new world power, The Empire of the Rising Sun, appearing on the scene, headed by the unusually serious George Takei (what does that say about the game?).
Cue the usual C+C base building, tank rushes, superweapons with daft names (psionic decimator anyone?), commandoes, and a istinct clothing rationing policy for female soldiers/staff. Whilst the gameplay is more or less the same as the original C+C, there's enough variety in the factions, units, and their special abilities to keep it feeling more like worn and comfy jeans you slip into rather than a knackered old pair of trainers.
As this was released 5 years ago, it can normally be picked up at a competitive price on Steam / online, and is well worth the outlay. Tim Curry and David Hasselhoff in the same game as Gemma Atkinson and Jenny McCarthy? What are you waiting for?