Skyline is unbelievably bad. It's so bad that you actually feel worse for the characters who don't die off early in the movie than for those who meet an early demise. The film seems to rely completely on special effects, but can't deliver enough to...

Solid VFX the camera doesn't shy away from ; Some neat concepts in play ; Twist ending ; Strong HD presentation

Budget went all to VFX and it shows ; Cast is utterly unforgettable ; Lacks an epic scope given the concept ; Hardly any VFX bonus features

I'd say avoid Skyline like the plague but those visual effects are worth a look, especially on Blu-ray where Universal has punched up its presentation and package more than it deserves.