How do you think Robert Downey Jr. will do as IronMan?

I'd say he'll do awesome.

After recent attempts at comic book films I'll hold off my remarks until I at least see a trailer

Let me word it this way...Downey will act well.

What do I mean, exactly?

I think Robert Downey Jr. will act "the part" as he should. HOWEVER, what truly matters is if Favreau and the script writer and the producers give him the right resources to work with. If they pester Downey to play Stark as someone that isn't like the Stark we are used to, it isn't his fault that he has to play it in a different light.

So...it all depends on everybody else. He isn't an unknown, so we know that at the very least, he understands that there are different characters that have to be acted out differently...