So is this a reboot?
Not really... it looks like they sent Kyle Reese back to save Sarah, but since it already happened, they have a T-800 to fit the first T-800, but there's also another Terminator, not sure if it's a T-1000 or newer version, in the mix.
Considering the last two Terminator films ranged from "meh" to "what in the actual hell is this," they might as well reboot the franchise. The trailer made sure to shoehorn in every single reference to T2 as any other franchise reboot would anyway. I'll see it but I think my expectations are going to be really, really low... this is already coming out in a packed year and has to compete against Avengers, Star Wars and what looks to be a great 007 flick.