The pretty night time setting, the way the invaders float towards the sleeping city, the almost leisurely way in which you fire off shots... Refuge really is almost dreamlike.
In terms of play mechanics, it shares most with Missile Command. Your turret cannot move, for a start. Also, once you hit an invader, if they then hit a fellow enemy it'll take both of them out, possibly triggering a chain reaction that to a certain extent mimics the hit radius of a Missile Command shot.
I just kinda like the vibe though.