Something about his hair/eyebrows/John Krasinski
His hair just doesn't suit his face in Chuck, it just looks odd. Some episodes
it looks like it's fine when it's allowed to be styled, but the Nerd look, his eyebrows are just too chiseled which directly contradicts his hairstyle.
Looking at his IMDB photo, you can see his eyebrows fit his RL hairdos.
The mannerisms are almost uncanny if you compare them to John Krasinski of the office.
This actor could be replaced by John Krasinki and it would be a dead match for this role.
Not saying I hate this actor, just some things I've picked up marathoning seasons 1 & 2