I like DS9 because the characters are flawed. Sisko isn't some confident paragon like Picard. He starts the series a broken man. Kira was a terrorist, Odo helped out during the occupation, Bashir lied to get in to Starfleet and don't get me started on Garak...
The flaws and different facets are what make these characters so much more interesting than Geordi LaForge, Dr. Crusher or Troi.
Flaws are ok, as long as they don't make them unsympathetic
. The problem I have with DS9 is that the flaws the characters have make me hard to empathize with them. Bahir's personality was also very grating, and Avery Brooks spoke like a robot. Odo was probably the most likeable character, even though he walked around perpetually annoyed.