I'm a fan of Samsung digital cameras. It's not that they are exceptionally great, but they're pretty darn good and reasonably priced. Yes, you can do better... for a price. And you can certainly do worse... and pay more.
Actually, Samsung does a good job of smartly designing their cameras. They may be the best in the industry at that, in fact.
The NX300 is nothing more than an NX210, but a little smaller, faster, more flexible (as in the rear screen is movable) and is capable of 3D video and images.
Perhaps the biggest improvement is speed, which, if true, will eliminate one of the "negatives" of Samsung's previous models. When saving in RAW or focusing in low light, the NX210 and especially the NX200 are not the fastest cameras out there. Supposedly Samsung fixed those issues with the NX300.
The movable rear screen is a good addition. It's also a touch-screen, providing another way to access features. Hopefully that won't increase the yet-to-be-announced MSRP too much over the NX210.
I think the 3D video and images are a gimmick. People will buy this camera for that, but probably won't find themselves using that feature often. It's not as if 3D TVs are in most people's homes. And by the time they are, it will probably be a different format that isn't compatible with files from this camera. And you can't make 3D prints.
Samsung has not announced when this camera will be released, but it will probably be around March or April.