I liked Kaidan because my main femshep was almost fully renegade and yet he still fell in love with her, still thought she was something special. I was convinced she was going to end up a loner but he didn't mind the reprimands, the sarcasm or the brutal murder of various NPCs. (He's a sweetheart like that.)
I ended up really enjoying thier dynamic, it was like a reverse cliche of the tough brutal macho man falling for the kind, idealistic girl back home that reminds him what he's fighting for. For my Femshep, Kaidan is the temperence to her chaos, and for all her aggression and rough persona, that little moment before she headed into the Omega 4 relay when she looked at his picture on her desk and smiled, it was that little glimpse into her heart, just totally perfect.
I'm sure as a Paragon that Shep/Kaidan is very sweet, but now I couldn't imagine playing the romance any other way.