It is indeed short, probably 3 - 4 hours to complete nine missions. Those who like to run and gun with little interest in collecting intel or exploring the levels will lean closer to 3 hours.
Those who like to explore and wish to make the most of the game and its presented challenges will get a lot more out of the campaign, as not only is there intel to find and acquire (some of which requires stealth interrogations of high ranking enemies, which means you'll need to silently isolate them), but every stage also has three optional challenge modes that present you with a set of completion criteria. For example making your way through stealthily with X weapon while collecting Y intel, or getting X kills with Y weapon and performing several triple kills. The themed challenges spice up the campaign kind of like GoldenEye's extra objectives.
If you're a hit-and-quit style player who won't stick around for replays, the campaign has less value.