Until ROTS, the tactics of the Clone troopers was really no better than that of the droids. And in ROTS we see them taking HEAVY losses in combat against droids.
What shows them having success in AOTC is the element of surprise and their big guns that seem to be able to blow up droids in one shot. Of course droids can kill the clones in one shot as well, with weaker guns, so there you go.
It's all well and good to say that Clones are superior to droids (the only evidence for that we have in the movies is Lama Su's word for it, but he could just be exaggerating due to pride and to promote his product), but if the EU (Prior to this most recent retcon) is to be believed, they still should have lost, because there's no way that a few million soldiers can win a war against "quintillions" of soldiers even if they are slightly inferior, or even if every clone kills 2,000 droids each (even quadrillions is insanely impossible odds).
Still, even with the retcon, the Clone Wars turn into a tiny skirmish, not a galactic scale war as the movies depict them and we're supposed to believe. And if Clones make up such a tiny portion of the forces involved, why name the entire war after them (as Yoda does after the first battle)?
Given the EU situation (pre retcon), the CIS losing beggared belief, despite Palpatine's meddling and alleged Seperatist incompetance and alleged Clone soldier l33tness...
Now it just makes the war look pointless and inconsequential, far from the epic scale it was always intended to be. I think this is a solid example of EU writers basically all but ruining something cool from the movies. Oh well...
I mean, watching the movies and just forgetting the EU stuff while you do, you get the impression that the two sides are pretty evenly matched, with just some strengths and weaknesses on both sides with fairly even numbers (we just have to assume that "1 unit does not equal 1 individual soldier, otherwise the droid factories if they're all like Geonosis would far outproduce the Republic in short order), and what REALLY changed things was that Palpatine had "fixed" the sides and was playing them both against each other by controlling the top leader (Dooku) and manipulating everyone. THAT was believable, this other stuff that came later... not very much so.