The story is the cliché. Some old time friends in high school want to create a club. They have some difficulties starting the club because they must find a new member. After finally gaining this new member they prepare for competitions. There is also the premise of the old friend who has turned angsty and works as a somewhat-antagonist. Of course there is the extra array of fanservice and splashes of shounen-ai inferences. The show is also fairly humorous. Besides the cliché plot, though there are some good features. I personally enjoyed the little comments that Haru would make about water and how it is alive. These were insightful and poetic giving the show a small amount of substance.
One word: Pretty. Being a girl the art is extra appealing since it involves the more-often-than-not bare chested men. I'm not going to lie by saying that this was not the main reason why I continued watching the show. Even without this though I still found the art pretty. The colors are nice and I loved the animation for both the opening and ending. Paired with what I said in the last paragraph about Haru's insightful words about water, I also love the scenes where Haru is shown to be drifting under the water. It is as if he is one with the water and I just really liked that. The anime counter parts for each character was both cute and discouraging. It was cute when it was just small references but the last episode pushed it too much.
I love the opening and ending songs for this with a passion. This is only the second anime I have watched that I watched the full ending video every time (the other being Mahou Shoujo Madoka Magica). As for voice acting I am not a good judge. All I can say is I liked the voices.
The characters all pretty much had a "thing" and that was mostly all there was to them. The characters are likable but not very rounded. Here is a list of each character's thing(s):
Haruka- obsessed with water, obsessed with Rin, only swims free, shows little expression
Makoto- worries about Haruka, small sweet smiles
Nagisa- obsessed with Rei, energetic, pushy, childish
Rei- obsessed with beauty
Gou/Kou- obsessed with muscles
Nitori- obsessed with Rin
Amakata- quotes out of place, embarased about her past job
There are some more characters but that is pretty much all there is to the characters. Even though he is not my favorite I would say that Rin is the most developed character. There are reasons for his moodiness which round him more than the others.
Overall, this is a good watch for fangirls who want fanservice or new yaoi ships. It is also good if you enjoy sports and/or the themes of being a team and friendship. If you are wanting something with unforgettable characters or plot this is not the anime for you. I would recommend you look up the opening and ending songs though because they are catchy.
Updated review at http://www.bubblews.com/news/2011049-free-iwatobi-swim-club-review