First off, I don't see how you can say 24 didn't put a bit of mystery around some of their characters. There were plenty of characters throughout the seasons of 24 where you weren't really sure if they were "good" or "bad". Not too many people thought of Nina Meyers as a "bad guy" until much later when she was actually shown to have been a mole (and a little later on, a murderous sociopath). A lot of the characters were also shown to be more complex than just good or bad. A lot of the people in government positions who did bad things, such as Walt Cummings and President Logan, did what they did because they thought it was best for their country. Their actions may have been wrong morally, but we do generally believe it's right to do what may be in the best interest for your country. If you think Cummings and Logan were clearly "bad guys", then you should probably think the same of Jack Bauer... isn't his philosophy basically the same thing?
Secondly, based on your last sentence, you may be neglecting the number of episodes each season of both shows were. There were many seasons of 24 where a mole or a bad guy wasn't revealed until after 15+ episodes. Homeland is now just 11 episodes in. Yes, a season for Homeland is only half as long as a season for 24, but 11 episodes into a season of 24, you still had no idea which directions the characters and plots would go. Also, by the end of the season, 24 had to conclude most of their plot lines because each season reflected one day, whereas a season of Homeland can reflect a few weeks or more.
Finally, if you really need to believe that person A is a "good guy", and person B is a "bad guy", then feel free to do so. If you want, you can believe that everybody in the CIA is a good guy, and that Nick Brody, Tom Walker, and Abu Nazir are bad guys. It doesn't change the fact that you wont really know until the writers decide to make it clear one way or the other, and the same was for 24.
Edited on 12/15/2011 1:58pm