Arizona is a decent team, but only because they have a great starting rotation and solid bullpen. Their offense is one of the weaker offenses in the league, so Glavine's performance is not all that impressive.
I think that if he starts pitching better he might be worth a pickup for ERA help. However, don't expect WHIP help, because even in his prime, Glavine was a mediocre WHIP guy. Also don't expect the wins, because he won't get much run support and even if he leads with a win, the Mets terrible bullpen will most likely blow it.