Montembeault has been excellent in all three games.
Dobes has ice in his veins but may just be too raw at this point.
Dobes is what we call a "reflex" goaltender, ala Tim Thomas.
His positioning isn't conservative, at all, and he tends to want to box-out shots by aggressively covering one side or the other and coming after the shooter, a technique which has both pros and cons.
If Dobes' aggressiveness pays off and shots come from the side that he clued-on, saves become more routine and controlling rebounds is much easier. If Dobes moves too much in-net, or misjudges a shot's location, the opposing team gets ultra high-danger scoring chances and partial empty nets to shoot at.
All of which to say that knowing exactly when and how to take risks in-net takes reps/ years of experience, which Dobes is profoundly lacking in as only a second-year pro overall and NHL rookie.
So yeah, Dobes has some very good athletic talent, and tracks pucks incredibly well. Dobes may yet "figure things out" and become a #1 goalie.
He could also fail completely and bust, or end up somewhere in-between. We don't know yet, and that's the beauty of sports.
But chances are that Dobes' inexperience may spell trouble for Montreal in these playoffs.