A nice idea, but it doesn't exactly what Tolkien had in mind when he thought about the possibility of the Ring corrupting Gandalf. It must be remembered that Gandalf would use the Ring's power because he wants to do good and help people. That's how he would start. But due to the Ring's corrupting influence, he would eventually become increasingly heavy-handed and authoritarian with his interpretation of justice and rightness, and end up corrupting the very concept of goodness itself as the new god-king of Middle Earth.

In other words, he wouldn't look nasty and evil. He'd probably wear all white and look magnificent and regal. He just would roast alive anyone who might question if total genocide of every nation that once served Sauron might be a bit too much.