Despite the fact that KyoAni never intended for Free! to be anything more than a 30-second studio promo, I think they did an excellent and interesting expansion of the original clip. After the attention it got online they'd've been dumb not to take advantage of what was clearly a potential market--but it's still great to see a studio delivering such a grand product purely because the fans asked for it.
Brief Summary: Childhood friends Haru, Nagisa, and Makoto realize that their other childhood friend, Rin, is back from Australia. Rin doesn't seem to want to relive their glory days of swimming together in elementary school, but the other 3 decide to create a swim club at their school so they can all "swim together again." Cue various drama and a dramatic ending.
Story: Simple, yet refreshing. High school boys swim team is such a good setting for so many reasons--locker rooms, swimsuits, glistening muscles--I'm surprised that it's not a more common vehicle for shows appealing to the female audience. There's oodles of fanservice opportunities, and KyoAni takes advantage of many of them, but it never seemed to take itself seriously, or be unanatomical. (Although high school boys usually aren't quite so muscular, but I'll forgive them on that).
Animation & Sound: Bright and sparkling, good use of color, and smooth action scenes. I'm not picky about sound, but I enjoyed the voices & music.
Characters: They're not stunningly deep, but they work well with the plot and are consistent. The female characters were present, developed, and not completely goo-goo over any specific male characters (just Gou's muscle fetish, lol).
Overall: 7.9/10. This is a really solid anime, with much more depth of plot and character than is usually present in any show that even borders on shounen-ai. The fanservice is fairly tongue-in-cheek and not ecchi, which makes Free! a good choice for almost anyone who likes a good sports anime.
If you really despise anything with deliberate male fanservice or shounen-ai overtones, or are just not a fan of light school/sports shows, then this show is probs not for you.