Powerful, engaging, fun and tense. Gyllenhaal and Pena are both fantastic and work extremely well together. Their relationship is detailed and interesting to watch and the film is self aware enough to manage it well. On the downside, the shaky camera footage aesthetic adds little and the largely plot-less plotline only detracts slightly.
As a side note, given the great pains Ayer went to make the film realistic, seeing the protagonists survive a deadly ambush with only scratches was just irritating.