The Panasonic VX870 was well received for its video quality--along the lines of don't-fix-what's-not-broken, Panasonic introduced very small adjustments with the 2016 VX981.
Like the previous version, the VX981 can shoot in 4K at 15 fps. What's new is that Panasonic has added in-camera editing options. The high resolution of 4K opens up some interesting possibilities for stabilizing and cropping video without disastrous results. With the new in-camera edits, 4K video can be touched up and saved as 1080p footage, but with edits for stabilization and other options that result in better footage than recording in HD in the first place.
That's pretty much what Panasonic has changed over the older model. The VX981 uses the same 1/2.3" backlit sensor, so it should get the same solid low light video results. The 20x optical zoom lens is also fairly bright with a f/1.8-3.8 maximum aperture. Manual controls are paired with a focus control ring for more creative control over the footage. Hybrid optical image stabilization and a five channel mic are all included as well.
All of these features are packed into a camcorder that weighs less than a pound. The downside is that big capability in a small body leaves little room for a battery--the VX891 will record up to 45 minutes of 4K on one charge. Potential consumers should also be aware that 4K is only available in MP4, not AVCHD.
The Panasonic VX891 is a solid camcorder. While certainly not perfect, it offers excellent video quality and a good range of features at the $899 price point. If the new in-camera editing doesn't interest you, you can probably save some cash on the older Panasonic VX870.
See Also: Best 4K Camcorders