Currently chillin' at 77 on Metacritic (41 reviews), Killzone Mercenary seems to be a far cry from the rock-solid triple-A enterprise Sony were no doubt hoping for. It's got some 10s, but its scores run the gamut all the way down to a 5.5.
When faced with such division of opinion, look to those you trust - and because I haven't written a review of it yet (or played it, beyond a few moments with the beta), I suggest the final paragraph of Eurogamer's 7/10 review:
"Despite the addition of a second stick, the Vita has struggled to deliver an FPS experience worthy of note. Resistance: Burning Skies and Call of Duty: Black Ops Declassified were both turkeys, so the bar is pretty low. For all the small fumbles and compromises, Mercenary clears that bar with ease. A solid and visually impressive shooter, it never manages to feel essential - and clearly exists mostly because all first-party franchises are obliged to put in an appearance on a new console - but even as a relatively minor entry in its own series, it still sets a new benchmark for portable shooters."Hm. Y'know what? That still sounds pretty awesome.