The shows are the same show. One takes a fantastical approach and one uses terrorists.
Both shows work from the premise that a particular disaster, scheduled to happen by X time must be averted at all costs.
Both shows use the same basic formula: ensemble cast, plot-lines-o-plenty (some way more interesting than others), good people vs. the evil people, with simply preposterous twists and turns along the way.
Both shows have people with special powers. Heroes takes the superhero powers approach, whereas on 24 it's mostly fists, guns and guile. But when Jack Bauer says, "I'm not CTU, I'll go after Walt Cummings myself" with a look of contempt on his face, he IS pulling off a power most of us wish we could pull off: the power to say f-u, I'm going to do what I want anyway.
I like both shows largely for the same reason. Heroes is the more moving tale, but Heroes is also a tad more fictional.
