Stirring stuff, man.
I think "too far left" is silly. But, like, look at the MW. Right-wingers always respond to people saying "it should be a little bit higher than it currently is" with "why not make it a billion dollars an hour, then? Heh-heh." There's no evidence that a small increase would cause any problems. And $15/hr works fine in a rich city. But nationwide, that would cause a lot of unemployment for low-skill workers (that's especially in places with the weakest safety nets). So ideologically, there's nothing wrong with the plan--I think most people would like to see the poorest workers get an increase in their pay--but practically, it's not a good idea. Same thing with some of his plans for banking regs. It's not that there's anything wrong with the goals (so it's not an ideological issue), but he doesn't have a smart plan for attaining those goals.
If he wants to go hard left and expose people to ideas even if they don't have a great chance of happening right now, I think he should talk about national property taxes, shifting tax burdens from labor to capital, SS for children, aggressively targeting full employment--things like that. Where he's been going has been simultaneously too radical and not radical enough (not fundamentally changing the shape of our distributive institutions but making big changes along current lines that could have large negative impacts).
So, you know, I think Bernie is a really good guy (he attracts some awful followers, though), but I don't think he's ready for the big stage.