Hiya, I'm Plusle

This is just a personal reason for me, but I absolutely abhor the art style it's drawn it. It just looks like little effort was put into the drawing and animation; but that's just a personal opinion/bias and wouldn't expect others to see eye to eye with me on that.

You've kinda already touched on it, with the length that it is, sure it might start out decent but with longer animes, such as bleach, naruto and one piece, they tend to lose their direction and sense of plot. The creators can just kinda go all over the place- and due to the length of it, it's bound to get somewhat repetitive.

I feel that if you're going to waste your time watching 600+ episodes, there are many more animes that could be watched, and you'd feel better about your time spent watching them.

That being said, I am picky about my anime. I'll rate some of the shows I've watched recently:

-Steins;Gate: 9.5/10, I'd say even the dub of this is great if you're a sub-only snob.

-Puella Magi Madoka Magica- 4/10 Seems overrated. Plot was predictable for me.

-Darker than Black- Season 1~ 8.5/10 Season 2~ 6.5/10

-Blue Exorcist/Ao No Exorcist- 7/10, I felt it was kinda geared towards little kids, but pretty decent overall.

-School Days- 3/10, too boring, only real drama happened in the last few episodes

-Mirai Nikki- 7/10

Shingeki no Kyojin is on my watchlist, but tumblr is pretty much ruining for me with all the hype and such ;-;

The art style doesn't bother me too much; it's more of a length issue I definitely prioritize shorter anime first, though so I'll consider it :O

Haven't seen Puella Magi Madoka Magica, but after reading the synopsis I don't think I want to

Haven't seen Darker than Black either, should get onto that soon.

Seen Ao no Exorcist, School Days (eh, I actually cut to the end because the first few eps were boring as hell) and Mirai Nikki. I'm reading SnK at the moment, but I haven't been watching the anime. It really is a good series! Follows strictly to the manga so far.

If you haven't already, consider watching Phi Brain (currently on 3rd season) and Psycho Pass (currently on 2nd season). I'm waiting for Psycho Pass to finish before watching but I couldn't wait with Phi Brain... ^^;

And I'm not sub-exclusive; some dubs are pretty good, like FMA:B. I just tend to watch subbed cos' it comes out earlier.