I quite liked the first two episodes, it's bubblegum sci-fi but unfortunately that seems to be the only sort of sci-fi we'll get for the moment. Maybe my expectations were lowered by the awfulness of Falling Skies.
Main thing that bugs me though, they sent a probe back through the time portal thingy, then when they didn't dig it up in future they concluded that it must be an alternate time stream or something so sent people back. That's one hell of a leap of faith, especially since sending people back could mean something happens to the probe. Oh well, that's always the problem with time travel plots I guess.
Oh yeah the wimpy guns were a bit of an issue too - what were they firing? rock-salt?