The photo that says it all - LEGO, Marvel, and DC, all together:
Let's start with DC. Even though we've seen four of these characters previously in the Batman line, these are all new prints. Catwoman and Batman are pretty similar to the previous versions (Catwoman just has some printing to make her look curvier, and the logo on Batman's chest is the variation with the yellow oval around the bat, where as before it was just a slightly larger bat). Joker has a more detailed vest and a different hairpiece (the Count Dooku hair mold rather than the vampire hair mold). We've actually seen a green version of that hairpiece before and it's been used in Joker customs. To me the best of this bunch is Poison Ivy, as the newer fig is a great improvement over the older one and not just a minor variant. Turning to the all-new characters, both Wonder Woman and Superman look amazing. I particularly like Diana's hairpiece and golden lasso. My only minor nitpick is that they should have printed WW on a fleshy torso rather than a red torso, but maybe LEGO thought a nude-backless fig would be too risque?
Now turning to Marvel, these are obviously preliminary figs, as none of them are in finished form (e.g. they're all stickers rather than printed figs, Thor's hair, no face on the Hulk etc). Captain America is the star of this show, IMO, as that fig looks perfect. Thor's hammer looks great, and I'm going to need a couple of extra ones for my castle-theme dwarf blacksmiths. I have to say I particularly dislike the Iron Man mask. A Flickr commenter referred to him as Bobblehead Iron Man and I agree. They should have gone with a printed head or a much smaller molded head (e.g. like the C3PO fig) rather than this huge mask to fit over a normal fig head. I'm not going to let that spoil the fun, though, as I'm sure I'll get this fig as well when they come out. The hairpiece on Wolverine is an obvious pick, and we've seen very similar customs in the past. It looks like his claws have a little post that he then holds in his hands - kind of similar to the claw weapon we saw in the small Prince of Persia set. Hulk looks a bit like the old Rock Monster to me, but I really like the molding around the neck and that hair (I wonder if it comes off). Not sure why they didn't get the face painted by the time of this display.
The exclusive Green Lantern and Batman figs are limited number (1500 each) free raffles. I'm sure these things will cost an arm and a leg, and maybe another arm, on the Bricklink/eBay secondary market.
Here we see what they meant by 'buildable fig' in the press releases. These seem to tie to the Hero Factory line (the successor to Bionicle):
Here's the teaser video from the LEGO Super Heroes site (also on YouTube and around the web).
A bit of an afterthought, but the Marvel partnership press release is now posted on Lego.com. I'm not sure why this was delayed a day after the DC press release, and this seems a little bit of a screw-up. Key information in this is the list of upcoming figs:
The LEGO SUPER HEROES Marvel collection will spotlight three Marvel franchises – Marvel’s The Avengers movie, and X-Men and Spider-Man classic characters. The LEGO Marvel’s The Avengers movie line brings such ever popular Marvel characters as Iron Man, The Hulk, Captain America, Thor, Hawkeye, Loki and Black Widow to LEGO minifigure form. The LEGO X-Men collection includes minifigure comic versions of Wolverine, Magneto, Nick Fury and Deadpool, while the LEGO Spider-Man sets offer minifigure comic versions of Spider-Man, and Doctor Octopus. The first buildable characters in the LEGO SUPER HEROES collection are highlighted by Captain America, The Hulk and Iron Man.