To Aru Majutsu no Index (or TAMI for short) is the very definition of a generic anime. Theres nothing good here but its not necessarily bad. Some characters are likeable and entertaining but that makes up such a small percentage of the enormous cast that its just not worth it. TAMI is about a guy named Touma who lives in a city thats entire purpose is being a school for Espers (see: Psychics) although nobody actually reads minds and its more they all have a certain power. So nobody is psychic at all. Touma discovers a young girl hanging on his balcony whos a magician being chased and he helps her. They become friends and have adventures. Thats TAMI in a nutshell, they tried having some main story throughout the whole thing but nothing important was revealed and the series couldnt keep a story arc going past 3 episodes. And thats where this show really falls to mediocrity. By constantly changing the focus of the story to some new threat and introducing 1-4 new characters every 3-5 episodes you lose the whole point of this series.
The characters themselves are just so two dimensional and uninteresting that you dont care for their story at all. Not to mention they all have to have some gimmick to distinguish them from another character.
As far as genre goes TAMI is a shonen type action show but thats being too generous in my opinion. TAMI's action scenes never go past 1-3 actions before they have to talk for 90% of the fight about something that wont even matter once the conflict is resolved, and all the main character ever does is punch people.
TAMI isnt necessarily bad but its just so plain that you find yourself wondering why you're even bothering with it? It tries to be funny but always throws the same gags at you that you just dont care for them. I think theres some wasted potential here and thats a shame because I really wanted to like this show