Post a series 你 think started off well, but went downhill and disappointed you.
For me, it's Mushishi. The first episode was great - really cool and interesting, not to mention I instantly liked the main character, Ginko (he's like a 交叉, 十字架 between 卡卡西 Hatake from 火影忍者 and Snufkin from The Moomins - i.e. he's awesome), but after that... it got rather repetitive. All the episodes pretty much followed the same structure and there was only one episode that ever actually revolved around Ginko. The rest were about the people he helped, who were all as boring as the average 火影忍者 filler character. In fact, they basically WERE filler characters. Such a shame; it had so much potential... I 爱情 the mood of the anime, so relaxing and peaceful... but there was no progressive story line, it was as though every episode was a filler and that just put me off. :/