Elon Musk said on a conference call with reporters that the launch "seems to have gone as well as one could have hoped with the exception of center core. The center core obviously didn't land on the drone ship" and he said that "we're looking at the issue." Musk says that the core ran out of propellant, which kept the core from being able to slow down as much as it needed for landing. Because of that, the core apparently hit the water at 300MPH, which should be worth seeing on video. "We have the video," Musk confirmed, "it sounds like some pretty fun footage... if the cameras didn't get blown up as well."
This shouldn't take away from SpaceX's spectacular achievement today . The goal of this demo launch was to prove that the Falcon Heavy was ready for flight, and it more than accomplished that. Landing the first stages is always a secondary objective, and no one should overlook the fact that the company was able to land two of the three boosters at once. SpaceX will likely learn quite a bit from this failure, and be better prepared to land all three boosters next time, which will probably be in three to four months.
Nathan Ingraham contributed to this report.