If you were expecting something straightforward, you've got the wrong series.
Hideo Kojima took the stage at the 2013 Game Developers Conference to talk about Konami's new FOX engine, though you wouldn't have recognized him. With his entire face wrapped in protective bandages, he was indistinguishable from the mysterious character we saw in the trailer for The Phantom Pain - a game that had always looked suspiciously Metal Gear-like. As it turns out, the collective hunches of the internet were right - Kojima hit the play button on an action-packed trailer for none other than Metal Gear Solid V: The Phantom Pain.
We had a few pieces for this particular puzzle already. The trailer included previously seen footage from trailers for The Phantom Pain and Metal Gear Solid: Ground Zeroes, but now we have a more complete picture. That's not to say we have any idea what's going on. We see Snake regaining consciousness in a hospital after a nine-year coma. At some point everything goes to hell, since we've seen plenty of Phantom Pain footage depicting an injured Snake escaping from some kind of raid on the hospital. Sometime after the escape, when Snake has recovered from his condition, the game shifts from this linear storyline and the world opens up for tactical free-roaming action.
There are plenty of new sights to see in the new trailer, which is the first piece of media to officially acknowledge Metal Gear Solid V's existence. A slew of characters who look pretty important show up, but knowing the importance of cloning and deception in this series, it's not very helpful to speculate based on appearances (but for the record, that totally looks like Ocelot rescuing Snake on the horse). There are some serious supernatural elements as well - we see another clip of the giant demon-whale eating a helicopter, as well as some horseback combat against a flaming figure riding a fiery, nightmarish unicorn. As for how any of this fits into the game's plot, your guess is as good as mine. We have a couple hints, at least: quoth the video, "From FOX, Two Phantoms were Born." Snake also has a brief line of dialogue referencing a group called the Diamond Dogs, which apparently is his "new home." And somebody named V is awake. Have fun putting that together.
It's worth noting that, yes, the trailer is very pretty - after all, it was debuted in a panel on the power of the FOX engine. We still don't know what the exact relation is between Metal Gear Solid V, Ground Zeroes, and The Phantom Pain, or if they're even separate products at all, but Kojima just let the biggest cat out of the bag so we'll probably be getting more details soon.
UPDATE: Kojima has taken to Twitter to clarify how all these titles fit together. "Ground Zeroes is a prologue of MGSV," he explains. "9 years after that event will be The Phantom Pain." The actual product of Metal Gear Solid V will cover both of these stories, not unlike how Metal Gear Solid 2 started with the prologue on the Tanker before switching to the main story.