Oh, I doubt it'll do much more than 240, and it's not a happy result, but it's not a flop, either. I don't think it's due to the quality of the film, necessarily, or even the response to the first, though that is a factor.
Really, at this point, we're entering a point of genre fatigue. Even with Marvel's continued success, there are a ton of superhero films getting released. Last year had four. 2012 had three. 2011 had four. This year will have four (or five, if you count BH6). And it's only going to get worse. If Marvel continues at their two a year pace, and continues their plans to ramp up to a movie every year, and Sony does the same as they've indicated. AND WB gets their program running so they've got a movie or two hitting every year... we'll be looking at 5+ superhero films every year.
Something has to give in that regard. Audiences may like the films, but nothing lasts forever, and eventually interest is going to plateau. Sure, Spider-Man was king, but this is the fifth film about just him in in twelve years. He's had the longest sustained presence of any superhero beside Wolverine (and even he basically had a gap of six years between the two solo films.) It makes sense that Spidey's going to be the first to feel some disinterest.
Nothing lasts forever. If it did, westerns would probably still be the biggest hits around.