James Hibberd

Just how important is tonight for NBC?

It’s the official start of the fall broadcast season and NBC premieres “Chuck,” “Heroes” and “Journeyman.” That’s half the network’s new dramas and its biggest returning show.

The giant “Heroes” buzz machine is dimmed only by its May season finale, which disappointed some viewers (muddled writing, character fates unclear, anticlimactic staging). The relentless summer marketing for the show has likewise felt like the old song, “How can I miss you when you won’t go away?”

Still, industry oddsmakers predict a home run. The fate of “Chuck” and “Journeyman” are less certain. “Chuck” has the buzz; “Journeyman” has the lead-in.

Aside from NBC, executives at other networks, in a weird way, are also rooting for “Heroes.” With broadcast ratings continuing to degrade and “flat is the new up,” nobody wants to see a smart, young-skewing sophomore drama that’s mostly done everything right come back to a Nielsen face-plant. If “Heroes” drops, what does that mean for the industry as a whole?

Also tonight: Eyes will be on Fox’s “Prison Break” and “K-Ville” to see how last week’s performance holds up against heavy competition. ABC gets into the fall game with the return of “Dancing With the Stars” and “The Bachelor.” CBS’s comedy block returns with the addition of “The Big Bang Theory.”