You should never just only look at the highlights of someone's resume. It should be about their ability to do the job, in terms of skills and talent.
That said, I'm personally not super impressed by someone having a political career. Success in politics is mostly connections, hard work and sales-skill. But, when you're talking about the Presidency, you don't just want a good salesman who has great rolodex a swing state. That's a type of skill I guess, but it doesn't speak to your character or your brain.
The President should be an exceptional person. With someone like Barack Obama or Hillary Clinton, that's not a question. Hillary or Barack could be one of the top corporate lawyers in America. They could be CEO of a Fortune 500 company. They have that kind of resume and intellect. Love them or hate them, that's true.
Is Scott Walker that type of person? I don't think so, but to be fair, I just kind of write him off because he's a squinty-eyed Republican dork. But, it doesn't matter what I think. I just think Scott Walker needs to prove himself qualified intellectually, more so than say, Barack Obama or Hillary Clinton. We'll see if he can do that.
Governors do have skills that are transferrable to being President. It's going from being in charge of a large bureaucracy to being in charge of an even larger bureaucracy (Walker's also made a similar leap before from County Executive to Governor.)
And before anyone suggests that George W Bush proves Governors make ineffective Presidents, he came from a state where Governors had to stick around for a long time to have an impact. Say what you will about Walker, he has been a consequential Governor.
Someone with the intellect to be a great corporate lawyer could still struggle in an unfamiliar environment, as Obama did. Hillary is obviously very familiar with Washington and how the White House operates, although this would be her first time in an executive position, where she's the one calling all the shots.