Actually, from what I know from using Gandalf in his ring-form, the grey one is utterly useless in my opinion.
He is ridiculously slow, weakens or at least fears allied units and apart from his ideed strong basic attacks his abilities are only... meh. Well, they certainly can do a lot of damage, but sometimes it isn't even worth using them because the basic attacks are stronger, then he has to get into range and the overall theme of Gandalf (tell the enemy to say goodby to his army) is fully fullfilled by the White Gandalf.
While this form has an incredible leadership which transforms your entire army into an ludicrously strong group and doesn't make him completely impossible to ever dodge catapult fire or (most import part) RUN AWAY! Because as strong as his attacks are Gandalf dies rather quickly and the Cursed is completely done when he has to run (which he isn't physically capable of doing
).
You see there are a lot of different ways to this topic. Also, just as a proposal for the future: Could you chose some more meanigful names for your topics? This discussion is literally only about the ring-mechanic of Gandalf, "About Gandalf" tells close to nothing about your intention for this topic.
Greetings
Melkor Bauglir