The second season of Heroes ended up being a bit of a mess, in large part because of the writer's strike that occurred that season, causing many of the planned storylines to be thrown out and never followed up on (in large part because of negative fan response). As a result, the season ended up being just 11 episodes, and kind of bounced all over the place in terms of the story. The season picks up four months after the battle with Sylar, stopping him from killing the cheerleader and saving the world. The story bounces between feudal Japan, the present, and the future, but unlike the first season storylines, it never felt, really until the very end, that any common theme or purpose was tying them together. And, by the time that started to be fleshed out, the season ended because of the strike. Hence, the series started to lose viewers, which continued until its cancellation after season four.
Even though the storylines were not as good as in the first season, which was, in my opinion, one of the best seasons of a tv series ever, the acting continued to be strong. The main cast, including Milo Ventimiglia, Jack Coleman, Masi Oka, Greg Grunberg, Adrian Pasdar, Hayden Panettiere, Ali Larter, and Sendhil Ramamurthy all returned. As does Zachary Quinto, and some of the season one recurring characters. The main additions to the cast this season are David Anders (from Alias), Kristen Bell, and Dania Ramirez. Christine Rose also came on as Nathan and Peter's mother Angela and pretty much stole every scene she was in. Her involvement was not huge in season two, but it would be increased in the subsequent seasons.
For extras, there are commentary tracks on each episode, a bunch of u-control features that allow for PiP viewing, and getting summaries of character arcs. There are deleted scenes and behind-the-scenes featurettes on each of the four discs. So, there is a lot of material if you want to watch it. The commentaries generally rotate members of the cast and crew and some include the series creator Tim Kring. They range in quality and tone but are generally good if you like listening to them.
Overall, the season is not as bad as it gets hammered for being, but not as good as the first season. Some of the problems with the season stories were within the writer's control and some most definitely were not. That said, I do believe that it is worth watching if you temper your expectations.