In just about every sense, the Surface 3 is a Surface Pro 3 Lite. It's smaller, lighter, slower, and cheaper. It will appeal to the same constituency that the Surface Pro 3 appeals to—OneNoters, digital artists, desk-bound mobile workers—but with markedly greater affordability and portability. It's a slightly worse laptop than the Surface Pro 3 but a somewhat better tablet. Many people will be able to find it useful.
One thing I haven't mentioned is lapability. That's not because the Surface 3 finally fixes this long-standing gripe; a laptop with a stiff hinge is still better for use on your lap. Rather, this is a system that's priced more or less as a (high-end) tablet or mediocre laptop, not an Ultrabook. As such, I never felt that I was using something lesscapable than comparably priced machines; in fact, the device felt like something more capable. Even if it isn't quite as good at being a laptop as a real laptop, it's much better at being a tablet, or at fitting in a backpack, or for watching movies on a plane, or as a sketchpad with a stylus. Using the Surface Pro 3, I always had a nagging sense of "I could get a nice Ultrabook for this money." I couldn't get something as nice as the Surface 3 for the money.
Surface 3 review: Smaller, slower, cheaper… better? | Ars Technica