I was thinking about this today, and since I haven't watched all the mecha anime titles there are (some Macross, some Gundam, Rokushin Gattai, Voltron, Gordian, Golden Lightan, Tetsujin 28), I can't say for certain whether the Transformers story (specifically the US cartoon) revolutionary for its time.

Most of the mecha cartoons have the robots as non-sentient power suits of some sort (e.g. Gordian), or whilst sentient, they don't really transform (e.g. Rokushin Gattai). I suppose the lions of Voltron sort of "transform" when they merge, but not really ... it's not as if the transformation allow the lions to function as something else apart from the purpose of the merge.

Astro Boy seems to be an interesting oddity in that he is sentient (but can't transform). Closer to the Transformers would be the robots of Golden Lightan, they essentially transform from cigarette lighters and into giant robots. But if my memory is correct, they are not really aliens in the sense that the Transformers are (a race of sentient robots from a metallic planet).

In my opinion, not only was the Transformers cartoon story creative for its time, it was even revolutionary because the origins of these robots were so different and more complicated than the robots of other cartoons.

But since I haven't seen all the mecha cartoons there are (I think there may be many more), I want to see what you guys think?