Story:
Ika Musume features short, cute stories (3 per episode) and most of them are stand-alone. There really is no plot, aside from Squid Girl wanting to invade humanity and failing, but it is incredibly entertaining and I loved every minute of it. It is one of the few comedy anime to make me burst out in laughter many times over.
Art/Sound:
The art is, again, cute, and Squid Girl's design is very memorable. Both the Japanese dub and the English dub are good (quite surprising), and the OP "Shinryaku, Ika Musume!"/"Let's invade!" is probably one of the most comedic and memorable OPs that I have ever seen. I loved it!
Character:
Though there is little character development, each character has a distinct personality, and you can always count on them to follow their norm. It's enjoyable to see them thrown into odd and funny situations again and again.
I love Ika Musume, and I'm sure you will too. ;)
