Do you mean via sideloading or independently of the marketplace? No- the MS team vets all submissions in much the same way as the Apple App Store. It's an extra step for a dev, but as an end user, I've been happy with it: no malware, much fewer bugs/issues than with Android.
For advanced users, there have been some official ways of unlocking devices for sideloading and playing with your device via MS and the Chevron team, so if you really want open access to your phone, you can actually get it- offcially even- no need to hack the bootloader and load a custom ROM