Still too me he some times comes of rather stiff and not getting the humor that Ianto is supposed to have.

'I guess, because some episodes he is in charge and strong and others he's like a shy girl'
Yeah, but then when has Torchwood ever been known for it's continuity. Depending on who is writing which episode you can have Ianto/Jack (KKBB), Jack/Gwen (Something Borrowed) or neither (From Out of the Rain).