Dano has been very diligent in posting new set pics to his Flickr, so all credit goes to him for noticing that the PoP sets are all now posted on Amazon to pre-order for April 1 release. Follow the links to Amazon for the ability to zoom in and look at details, plus another view of each set. I'm also linking to Dano as there are lots of comments there.
7569 - Desert Attack, 57 pieces, US$10.99 - Amazon, Dano

At $11 this seems like a must-have to get the new turban pieces, that printed horse, new hairpiece and three new torsos. Also very interesting are the new piece that allows the hero* to carry two katanas on his back and the bush piece in dark tan. Those wrist weapons on one of the bad guys scream out Wolverine custom fig.
*I have no knowledge of the video game or movie, so I'm just assuming this guy is the hero and the other two are bad guys.
7570 - The Ostrich Race, 169 pieces, US$19.99 - Amazon, Dano

Okay, this one seems silly to me, but maybe this is some key scene in the movie. I'm guessing, though, that it's more appealing to the younger set. Yes, the new animals are nice, and since there are two in this relatively cheap set I can see someone building an ostrich army. Turban in dark tan. Bare chested torso, but fleshy, two other new torsos. Otherwise not a lot.
7571 - The Fight for the Dagger, 258 pieces, US$29.99 - Amazon, Dano[url]
[url=http://www.flickr.com/photos/sirdano/4261392168/in/set-72157609751803566/]

In addition to that new helm, the turban in white, various new torsos and new female hair, look close and you'll see a new dagger. To me, though, that doesn't look very LEGO-y, just IMO. The thing that jumps out is, of course, the camel. Looking closer, this looks like a treasure-trove of architectural elements, with 12 or 14 of those new half arches, that new gold dome, a handful of cheese wedges and 1x1 brick with the stud on the side. I guess that canopy is also a new cloth element. Dano's got a great closeup of the new arch piece here.

7572 - Quest against time, 506 pieces, US$49.99 Amazon, Dano

To me, this is the big disappointment of the line. Lots of dark bley slopes etc I suppose, so good for basic castle building, plus six of the half arches, two lion head bricks in a new color, and those 2x2 tiles with one stud. I'd get the Fight for the Dagger, though, and just pay the Bricklink mark-up for the unique fig in this set.
7573 - Battle of Alamut, 821 pieces, US$79.99 - Amazon, here on fbtb's Flickr (not sure why it's not in Dano's stream)

As you can expect from the big set of the line, this has tons. Lots of those new arches, also in white (please, LEGO, can we get some in normal tan? how about the grays?), 7 figs, camel, three of those new helms plus one turban, wolverine claws, lots of bricks etc. Hmm, it looks like that dome from the Fight for the Dagger must be in four sections rather than one piece, since here we see it expanded with more curved bricks. The design is nice - the two side walls can swing forward on hinges to make one long flat wall with the gate in the middle, with a separate keep, or the walls can swing back and attach (though) the keep to make a square fortress.
Overall thoughts: This line looks great. Lots of new figs, with varied headgear. Camel and new arches look very useful. Other new elements maybe not as useful for me personally (dome, ostriches, wolverine claws), but I can see where those will be popular. I hadn't really mentioned the colors much - lots of tan, dark tan, dark brown, brown and that new rust(?) color. I do hope we see those arches at least in the more common colors, so they can be incorporated more smoothly into MOCs. I anticipate buying the small set and the Fight for the Dagger (maybe a couple of these), gazing longingly at the large set every time I walk past the LEGO aisle, and probably paying Bricklink markups for some of the other figs.