I'm not trying to be a negative Nancy here - but I think realistic/tempered enthusiasm is probably OK.
Most of the time, it's tough to come in with one year to play and tear it up. Usually it takes a little time to get a good grasp on a new offense and gain chemistry with the other players around you.
He might be really good, but still not have as good a year as he could if there were a second year.
That said, it wouldn't surprise me if he shows up and is good right from the start. But it also wouldn't surprise me if he shows up and it takes the first third of the season before he is most effective.