Essentially, the first two movies can be called a "recap" of the series, and can be downloaded online (obviously, I can't put up the links, find them yourself). However, saying "recap", I believe, understates the work Shaft put into the movies; the soundtrack and animation have been beefed up incredibly, so a better term would be "revamp".
I personally don't think that watching both the series and the first two movies are required; they both tell the same story, with the big differences lying in the visual, soundtrack, and the pacing of the story (some say it's worse than the series, I honestly didn't notice). The first two movies are, as one MAL reviewer put it, a "love-letter to the fans". Though they don't provide any additional material, it's satisfying for the devoted to see a refined Madoka on the screen. Of course, as one of the devoted, I found the two movies absolutely lovely.
The third movie is going to be a sequel off the main series, and honestly, it's the one we're most anxious about. Several fun facts and speculah flying around, but take them with a grain of salt, as always. You can bet I'll be at the premier.
This is a discussion topic for the three movies. Make sure spoilers are kept spoiler-taged.