I recently listened to the 30+ Tracks-Bootleg 'Complete Recording Sessions'. Its around 80 Minutes long and not boring at the least. Elfman employs its usual creativity in the percussion-section and mixes most tracks with electonic effects of every type and a quite sofisticated ethnical edge. The end result sounds interesting in its best places and at least a bit entertaining in its worst. Unfortunately, the quieter portions of the scores are only mediocre by Elfmans standarts. The simple four-note-theme heard througout the entire running time is not enough to carry the music. Plus, the orchestra isn't used to its full capacity with just a few notable moments of strength. As such, the score is a very good background listen but nothing you think about much.
For Elfmans' Standards this is only a weak score. (***) But compared to some (or most) MC/RC-electronically enhanced scores of late (i think of 'Deja Vu' or 'The Island') 'Proof of Life' has the egde, because Elfman is much better when it comes to the complexity and employment of his electronic/non electronic percussion (****)