The end is laughable - you'll enjoy this one.
So you'll know the majority of what happens from the trailers that have done most of our job - the first car out the lot gets trampled on by a big cow/rhino alien machine. We now know that was Turk's Ferrari. Somehow he survives the impact, gets off a few rounds, but then Jarrod actually blocks his friend's escape, and Turk's taken away.
The Apartment complex manager rescues them from a hunter alien, and we see the blue brains for the first time. We lose a few more citizens, and we're back in Terry's apartment where time moves very slowly.
Jarrod, having survived 'the light' a few times, is now empowered by it - and is slowly turning into The Hulk. The army show up to nuke the mothership - which goes down, but soon regenerates. Everyone seems unaffected by the radiation - and the manager isn't temporarily blinded even though he was staring straight at the explosion through a telescope.
The National Guard show up by chance on a neighbouring rooftop. Jarrod leaves with Elaine to get some help - but all they do is distract the poor soldiers bringing down a chopper and sending a few more souls off the roof to their doom.
Meanwhile, the blonde girl left in the apartment doesn't notice an alien slowly floating through the sky, and gets sucked in by the light. The manager decides to go out with a bang - and lights a gas stove scorching the monster rhino climbing the apartment block 'Rampage' style.
Another hunter alien picks on Jarrod and Elaine. Jarrod summons his new superstrength and goes at it with an axe and tears out a blue brain with spinal column from its insides. The mothership soon hovers overhead and they are both sucked up - which you'll have seen in the trailer so its no surprise.
Inside the mothership, robots are tearing heads off humans and pumping the brains into tubes to feed new monsters. I'm sure I saw something similar on a Simpsons "Treehouse of Terror" episode.
They tear the head off poor Jarrod, but stop when they find Elaine and see that she is pregnant. She is taken to a different 'room' to be experimented on. Jarrod's brain enters the tubes - but unlike the other blue ones, his brain is red. The brains are implanted into monster-aliens who run off to get busy with jobs - but Jarrod's monster tries frantically to get this brain out of his head - and then becomes self aware.
Jarrod breaks the robot arms keeping Elaine prisoner, and then in a scene stolen from Face Off does that 'brushing your hand over a partner's face' type trick. She assumes it is Jarrod, and not just a random, horny alien, and is happy to see him.
Jarrod steps back and prepares himself to save the day as aliens rush towards him.