Two things:

1) Power Shot is too hefty, especially in combination with deadly aim. If a rogue oicks this prestige class, at level 20 one has 33d6 damage(115.5 average), plus any bonus damage that might occur thrice. Four arrows of this, with the Fast Sniping ability, and basically every character one can imagine is dead after this guy's combat turn. Even if You limit it to maximum crit multiplier = strength multiplier, a character taking this class will boost strength to get it anyway(magically or otherwise)

2) You wanted comment on the gillie, You get it: Basically a good idea, but it has some flaws. First, You should designate a date of expiry for this, if one picks up parts of plants for concealment, these will rot in a few hours, a day at best, depending heavily on what materials are used. One option would be to state that a gillie lasts for one hour(or day?) per Sniper level, another option includes producing a terrain table where gillie durability is plotted over terrain type, the Sniper level would modify the durations on that table.
Secondly, a gillie should grant the Carmouflage ability, at least when the character isn't moving.
Also, what Hide skill penalties does the gillie reduce? Those on movement while hiding, I presume, but state it more clearly.