The preview, clocking in at over three and a half minutes, covers a lot of ground. It starts off with Green Arrow's origin, as callow young billionaire Queen is lost at sea and, after years presumed dead, is discovered and brought home to Starling City (rechristened from Star City in the comics). It follows Queen as he establishes his Arrow persona, confirming that the series will drop the "Green" from more than just its title. There's also a lot of soap opera type goings-on going on.
And if you look closely at just about the 3:22 mark in this video from SuperHeroHype, you'll see a very quick flash of a two-toned mask that will be familiar if you're a big DC fan.
That mask belongs to Deathstroke, aka Deathstroke the Terminator, aka Slade Wilson. Introduced as a nemesis to the Teen Titans in the 1980s, Deathstroke is a superpowered mercenary who has frequently butted heads with Green Arrow in print, notably in the six-issue "Identity Crisis" series by Brad Meltzer and Rags Morales. While not as well-known as, say The Joker or Lex Luthor, he's a popular DC bad guy, and the inclusion of his mask here suggests he'll have a major role to play on the show.
After a decade of Smallville came to an end last year, the CW is eager to get a superhero in its line-up of hour-long dramas, and this character, created by Mort Weisinger and George Papp, proved a popular supporting player on that Superman series. Arrow is, however, completely unrelated to Smallville. The series was developed by Green Lantern writers Greg Berlanti and Marc Guggenheim, as well as Andrew Kreisberg, who wrote the pilot teleplay. David Nutter directed the pilot, and the series is set to air on the CW Wednesday nights starting this Fall.
Here's an international promotional poster, courtesy of Green Arrow TV. Like so many theatrical one-sheets, this television poster includes stuff falling the foreground around our hero.