I'm a creature feature kind of guy. There are few things I enjoy more than a bowl of popcorn, a cold beer and a monster-of-the-week movie. So it goes without saying that BBC's Primeval - in which portals to the past unleash horrors upon modern Britan -- is my kind of show.
The pilot episode of the 13-episode Season 1 sees a variety of dinosaurs wander through into the Forest of Dean, including one particularly nasty carnivore that's taken to hunting the woods for prey (and the occasional tractor trailer). Episode #2 features giant bugs infesting the London Underground, while Episode #3 has a giant aquatic dinosaur prowling the nation's waterways.
Each has traveled through a rip in space/time connecting our present with eras millions of years in the past. And the portal's aren't one way; creatures (and humans) can pass back and forth between the two time periods. They have to be quick though; the portals are unstable, and time travelers can easily find themselves trapped in the past when one of the wormholes evaporates.

