2. Remember Jack's Limitations
The character of Jack Bauer aged ten years between the first and final series, and Live Another Day is set four years after the end of season 8, placing him in his early 50's. To expect the character to be capable of the physicality of earlier series would be unwise, though the sight of a wizened Bauer hobbling about on screen would also be ridiculous. The writers need to capture a fine balance, and have Bauer acting age-appropriate. This shouldn't be a problem in itself, Bauer was always a fine detective as well as field agent, so maybe we could see a few less fist-fights and a bit wore sleuthing? The writers also need to bear in mind that Jack was never intended to be superhuman, and did rely on help from other sources from the very first series. There was nothing more tedious in later runs than sitting back during a tense situation and knowing that Jack would easily get out of it by punching somebody very hard in the face. The realism must also extend to the rest of the show. The concept of time lapses between episodes should solve the conundrum of travelling during the plot, but instances such as Jack being stabbed one minute then merrily scaling walls ten minutes later doesn't work on any timescale.