He is a very good goalkeeper and always has been. Arteta wanted him as backup to Raya this season, so he is still good to go.
The reason people are excited is because an opportunity like Sze shouldn't really be available. Effectively, our poor squad planning should have meant the end of our season here.
He is not world class, but he is world class for what is available to us right now.
It's a tremendous stroke of luck for Barca. A keeper as good as him would not normally have been retired and available, proved by the fact that the next best available option is a half dead Navas.