Because of both Senate obstructionism and the relatively low priority placed on them by the Obama administration, the pace of appointments to the federal judiciary has been regrettably low. But quantity isn't the only issue. Under current norms, Supreme Court justices tend to come from the federal appellate courts. Particularly since the Reagan administration, Republican presidents have been very conscious of trying to put young conservatives on the federal appellate bench. This is how you get John Roberts and Sam Alito appointed to the Court at a young age. Obama, however, has yet to get a single appellate court judge under 45 appointed to the appellate courts. Since the inauguration of Reagan, "Republicans have appointed 41 federal appellate judges under age 45 to the Democrats’ 10."
Appointments to the federal courts are one of the increasing number of areas in which there is increasing asymmetry between the parties. For 30 years, Republicans have placed a high priority on packing the federal courts with young conservatives, while the Democratic administrations during this time have not placed a commensurate priority on getting young liberal judges confirmed. This might be OK if Democrats were gaining institutional advantages in other areas, but I don't see that they are. It's a real problem.