By Ian Youngs BBC News Online Entertainment staff

Jack Bauer may have just had the worst day of his life, but millions of viewers have finally watched the hour that the last six months have been building up to.

The last episode answered enough questions to avoid being an anti-climax, but left more to set the second series up nicely.

We now know that the terrorist who was plotting to assassinate presidential candidate Senator David Palmer failed, and ended up floating in the dock, sunk by several bullet holes.

Jack, the counter-terrorist agent played by Kiefer Sutherland, saved Sen Palmer's life twice in one day and was lucky to avoid death or nervous breakdown in a day that must entitle him to a lifetime of free therapy from the government.

24 revived Sutherland's career

His daughter, Kim, also lived to see another day despite being kidnapped twice and jailed once in 24 hours.

But his wife, Teri, was not so lucky and her fate provided much of the tension in the final episode.

24 was such a success because it broke old rules and created new ones.

The good guys do not always have to live happily ever after - Hollywood take note.

Teri died, and some of the good guys turned out to be not so good after all.

The revelation at the end of the penultimate episode that Jack's closest colleague and confidante, Nina Myers, was a traitor, turned the whole story upside down.

And it made for a tense, explosive, satisfying finale.

Nina said she was not just working for the Serbian warlord Victor Drazen, played by Dennis Hopper, who had appeared to be behind the whole nightmarish plot.

The questions fans will be mulling over until the second series are - who was actually behind it? And did Victor's son Andre, who we saw take a bullet, really die?

Come to think of it, was Teri really dead when we saw Jack cradle her in his arms before the credits began to roll?

There is no doubt that the 24-episode "real-time" format has been a huge success - and has made Kiefer Sutherland a star again.

Now get ready for a second series

The show was like a top US cop drama, but with the cliffhangers of a soap opera and the beginning, middle and end of a gripping action movie.

The large number of episodes may have required a few detours via diversionary sub-plots, but the whole point of the show was that there was one episode for every hour of the day.

Despite flagging three-quarters of the way through, when they suddenly introduced a few irrelevant characters and some pointless action, the producers kept viewers hooked remarkably well.

This was partly due to the unpredictable swerves in the storyline, which often came out of the blue and stretched the plausibility of the story but increased the necessity for fans to see what happened next.

The split screens and shaky, over-the-shoulder cameras helped the realism in a Blair Witch kind of way.

Work has already started on the second series, and viewers will want to pick it up again despite the draining intensity of the first season.

Whether Jack Bauer will be able to handle another day like that is another matter.