Like most people I was hooked on Season 1 with it's mysterious plot. Each week would reveal another piece of the jigsaw. I went into Season 2 with low expectation as I had heard on the grapevine that it wasn't all that good. However i only found it slightly less enjoyable. Season 2 still has the same format and surprises and enough to keep me hooked for the somewhat shorter season. If i was to be overly critical, some of the effects weren't as good (especially the flying sequences) and the whole story of Hiro ancient Japan seemed a little drawn out and unnecessary. Otherwise just as compelling as Season 1.
One of the few good things about the 2007/2008 writers strike is that it thankfully brought season two of Heroes to a far quicker end only comprising of 11 episodes compared to season one's 23 episode run. In reality season two isn't all that bad, the problem is that it lacks the focus of the first season, and splitting the characters up to pursue their own quests in different countries and timelines doesn't quite work as a whole and lacks the urgency of the season one's storyline. The result is still enjoyable and works more as an epilogue to season one than a series in its own right.