Headmasters is more substantial than Rebirth, and while you enjoyed that, it's too short since it's little more than a toy ad. I like that Headmasters gives more time to some of the characters which Rebirth only briefly showed.

My main gripe with Headmasters is how peripheral the Trainbots are - they barely even talk, let alone contribute anything ):

I agree that the callouts get annoying - but at least Headmasters doesn't have the long Transformation sequences like Armada onwards.

Masterforce is probably the best written of the Japanese G1 cartoons (and possibly all the G1 cartoons, so if you can through Headmasters, I'd recommend going for another series (: