I don't think it's possible not to love Simon. He's adorable and smart and kind of rings true for many of us awkward, shy people. If you like Iwan's work, you might want to check Vicious. It's a comedy with Ian McKellen and he plays a completely different kind of character.
I think Series One was much better. Not a fan of Alisha's plot line, I think the authors drop the ball with her.
Not a fangirl, but I usually divide characters I like in two groups: the ones I want to hug and give puppies to and hope life will end in sunshine and ice-cream for them (Arya, Shireen, Tommen, Bran, the Reeds, Jon, Theon) and characters that are awful and deserve pain and suffering but are so damn interesting to read/wath (Ramsay, Roose, Cersei, Joffrey). But I agree that show!Ramsay is more disturbing because of Iwan's portrayal.