In G1 when Megs got changed into Galvatron, his personality never really changed, he was still crazy, pyscho and power hungry.
In the movie, it's already been talked about that his agenda hasnt really changed. He wants "what's in Sam's head" he basically wants absolute power. I also read somewhere that he remembers the human that killed him off.
I think he is still has the same personality, just way angrier.