I watched the entire first half of the season, and only the first couple episodes of chapter 4. But it felt to me like the writers were fighting with each other, honestly - every episode would either change or flat-out ignore whatever plot- and character-developments had occurred in the previous couple of episodes. Sylar was a particularly egregious victim of this.

Also I got utterly sick of the whole "someone has painted/visited the future and now we must change it!" scenario. Three seasons in a row? Really?

I had a few more issues with it, but it's been awhile, so I'd have to ponder. That should get you started though.