Don't Call it Brooklyn Summerstage to their Face... ...especially since Celebrate Brooklyn! preceded Central Park Summerstage by about 6 years. Summerstage is great and all (see review), but I love Celebrate Brooklyn! It one-ups CPS in three ways: they don't bother you about bringing in food (at least they didn't when I was there), the acts are big names while the promotion is a little more low-profile than CPS (pretty much assuring that the place won't be completely packed 3-4 hours before the show starts) and the security presence is much friendlier. They actually seem to enjoy the music.
You're not gonna see Britney Spears at Celebrate Brooklyn! (I feel like I'm yelling by placing that exclamation point there, but hey, that's their trademark.) The acts tend to hail from "world music" or "fusion" or country or jazz or electronica or afrobeat or folk or roots or any other genre title used to box in good music.
Celebrate Brooklyn! is located about 15 minutes from downtown Brooklyn, in the urban bucolic synthesis that is Prospect Park. The easiest way to get to the Prospect Park Bandshell is to enter Prospect Park from the west side entrance. Take the F train to 7th Avenue.