Sentinel First Villain Or A Good Guy In Transformers 3?

During the war on Cybertron, the first Sentinel was already an intention to restore Cybertron to its former glory. Because of its ambition / intent, it made him mad and made a deal with Megatron for the love of his intention. During the time his ship was away from Cybertron feed technology that can teleport anything (Space Technology Bridge), it was already expected that it would meet with Megatron.

Now back to the topic, Sentinel Prime is a good guy or a bad transformer 3 Dark of the Moon? He was a traitor to the Autobots? He was the villain, then?