I just got done (literally, less than fifteen minutes ago) watching the English version. While it carries over a lot of stuff from the show, it's nothing like the first one in that regard by a long shot. It's still Evangelion, and it's still based on what came before, but it's much looser. The main story progression is going on, but restructured, reordered, and in some places heavily revised. With the second movie, they've pretty much gotten through episode 19 AND already introduced Kaworu. They've also introduced more Evas, cut out all the monster-of-the-week Angel confrontations, introduced and altered characters, and made Shinji not to be the utter pussy he was previously. So I would say, based on that, that the movies are a combination of the series, previous movies, the manga (YES!), and a number of new ideas on pre-existing material as well as brand new stuff.
In short, I think you should watch it.
As for Asuka's new plug suit, she's only in it for a few minutes, as it's completely new to her near the end of the movie. The funny part is, the last real line she has in the movie is something like, "one last thing...it's cool that it's red and all, but what pervert designed this suit? It's a bit revealing."