What @LimeBlast says.
I think this is something that is easy to misinterpret for all those who see 'The Lean Startup' by Eric Ries as their bible.
Yes, your MVP is an attempt to do the minimum amount of work possible to see if your proposition works. What I think is not clear in the book, is the need to not take shortcuts that result in a degraded user experience.
It's safe to assume, that no matter what your business idea is, there will already be people out there doing what you plan to do, doing it better, and already having traction. You are actively competing for customers against these people. Now, fortunately for you, your potential next customer may have decided to try you first, or may have some fundamental reason as to why they don't want to use one of your competitors.
Now, every barrier or hurdle your solution presents your customer with, that they see as tiresome or unnecessary, is one more thing that could send them back to Google and seeking an alternative.
So while the MVP is about doing the least amount possible, when it comes to user experience, it is absolutely paramount that you make it as fluid as possible. Avoid unnecessary steps.
So in this instance (and I admit, that I haven't taken a good look), I would expect to be able to browse around without having to register. Even if I need to register, gone are the days where you need to fill in endless forms. I expect to be able to click to sign up using my favourite social network. But even then, I'm not going to do that unless I think it should be required, and unless I'm carrying out some sort of transaction on your site (you might have convinced me to buy, or convince me that it's worth coming back, and setting up a few preferences), that I'm going to feel that registration is unnecessary.
So, if you're going to make me register, and I've independently reached the conclusion that I shouldn't have to, it's quite likely I won't and I'll simply go elsewhere.
Another perspective that is worth considering is Google. If all the good juicy stuff on your site cannot be browsed without being registered, then Google is never going to see it. Think of all that SEM you are missing out on!
I hope that helps a little.