I brought it when it was £7 and for that it was a good price. Really this game is about the eye candy as the backdrops and scenery are amazing. The gameplay is not bad and ok for a blast every now and again, there's only one weapon to speak of and melee and 3 types of 'grenade' so if you're looking for a weapons fest then give it a miss.
The fact that i've never played a FPS where you can float through space in all manner of orientations means you get disoriented very quickly makes it fun. Like I say, not a game you'll play for hours at a time, but a good blaster you can pick up every now and again and enjoy the visuals and sound effects. Even better if you can pick it up on offer as I would'nt pay more than a tenner for it tbh - £7 was about right.
EDIT: With the new weapons that seem to be coming along, it may actually become more interesting.