San Diego Comic-Con News:  A week before James Gunn’s Guardians of the Galaxy opens in the U.S., the director told (via video) a packed house at Hall H that a Guardians of the Galaxy sequel would debut on July 28, 2017.  The fact that Marvel already announced a Guardians of the Galaxy animated series and  let it be known that James Gunn would be back to write and direct a second Guardians movie demonstrates the studio’s faith in the property (see "Marvel to Produce 'Guardians of the Galaxy' Animated Series"), which Disney is merchandising heavily.
The July 28, 2017 date is one six new dates that Marvel has announced within the past week (see "Marvel Grabs Five Movie Dates," and "Marvel Grabs 'Amazing Spider-Man 4' Date"), as Marvel and Disney respond to Warner Bros. and DC’s more aggressive slate of superhero movies.
The Guardians of the Galaxy movie that opens next week continues to impress the critics--it currently has a 100% positive rating on review aggregator Rotten Tomatoes and analysts are predicting an opening weekend north of $60 million, which would be impressive for a property that had zero visibility outside fandom just a few years ago.