Booker has received a 95% and a 90% rating from the Americans for Democratic Action. So hardly a conservative. He's certainly charismatic and has a great life story (including the fact that he's been a Mayor, which most national figures haven't been).
Those are mostly measures of partisanship. For instance, Chuck Schemer, who loves to whore himself out to Wall Street, regularly gets 100% ratings.
And there's no doubt that Booker is quite liberal on social issues. He's just soft on many economic issues, particularly taxing/regulating corporations, especially finance.
He was the surrogate who went rogue in 2012 when he got mad at Obama for criticizing hedge funds (I actually thought that his defense of hedge funds was occasionally fair, his heart is just obviously in the incredibly wrong place as a senator from NJ)
