The best Anime series I've seen are:
(I define best as the ones that are very compelling and make you marathon the series)
Code Geass
Steins;Gate
Death Note
Fate/Zero
Fullmetal Alchemist Brotherhood
Kuroko no Basket
Cross Game
Gurren Lagann
Macross Frontier
Highschool of the Dead
Guin Saga
Phantom: Requiem of the Phantom
Madoka Magica
Welcome to the NHK
Clannad After Story
Blue Gender
Shinsekai Yori
Durarara
Bakuman
Samurai Champloo
Bleach (only the soul society arc, the first three seasons)
Fairy Tail
Neon Genesis Evangelion
Zetsuen no Tempest
Blood +
Claymore
Itazura na Kiss
Eureka Seven
Usagi Drop
Lovely Complex
(I define best as the ones that are very compelling and make you marathon the series)
Code Geass
Steins;Gate
Death Note
Fate/Zero
Fullmetal Alchemist Brotherhood
Kuroko no Basket
Cross Game
Gurren Lagann
Macross Frontier
Highschool of the Dead
Guin Saga
Phantom: Requiem of the Phantom
Madoka Magica
Welcome to the NHK
Clannad After Story
Blue Gender
Shinsekai Yori
Durarara
Bakuman
Samurai Champloo
Bleach (only the soul society arc, the first three seasons)
Fairy Tail
Neon Genesis Evangelion
Zetsuen no Tempest
Blood +
Claymore
Itazura na Kiss
Eureka Seven
Usagi Drop
Lovely Complex