UPDATE: As of today Visual Studio 2019 is available for download from the Microsoft website.
The latest edition of Visual Studio is almost ready for general availability (GA) and Microsoft has released Visual Studio 2019 Preview for download (Windows and Mac) to show us the latest improvements over Visual Studio 2017. Continuing after Visual Studio 2017, the improvements are focused on productivity, performance and a more cloud-oriented development workflow with easier ways to access cloud resources like GitHub and Azure DevOps Repositories.
The Preview enables you to run Visual Studio 2019 Preview next to your current production Visual Studio-version, so you can install the preview without risking your production setup.

Download the Visual Studio 2019 Preview and read the release notes.
UI & UX Improvements
Visual Studio 2019 brings some small changes in design and user experience. A more intuitive start window makes it easier to connect to cloud resources and create new projects, as well as an improved search feature that now allows for command execution and automatic correction of spelling errors. Debugging capabilities are enhanced by improving the debugging windows (locals, autos, watch etc.) which now have their own search feature.

Visual Studio 2017 (left) vs Visual Studio 2019 Preview (right)
IntelliSense is now AI-assisted
One of the most interesting changes for 2019 is that IntelliSense now has the capability to change the way it presents its suggestions by looking at your code and how it’s used. This smarter version of IntelliSense has gotten the name IntelliCode and its suggestions will show up with a star icon in the suggestion-list.
A simple example of this is that if you have class with a certain method of property that you use in most cases in a specific scenario (e.g. when iterating in a foreach-loop) IntelliSense will now give you that method or property as its first suggestion as opposed to an alphabetic sorted suggestion list. This means less searching in the suggestions and faster coding. IntelliCode does this by learning your code and creating a model of it, which you can share within your team.
IntelliCode is considered an experimental feature at this point but it is worth noting that you can install this feature as an extension in Visual Studio 2017 as well. IntelliCode does not ship with Visual Studio 2019 Preview unfortunately so you will have to manually download and install the extension.

After installing the extension, access IntelliCode via View > Other Windows > IntelliCode
Document Health
A new feature for Visual Studio 2019 is the Document Health-feature, which allows you to quickly see, as the name suggests, the health of the document you are currently working in. Via an icon in the bottom right corner of the editor you can quickly see if your document has any errors or warnings. This icon also enables you to quickly navigate to those errors by clicking it, and right clicking gives you options to configure and start your document clean up.

Live Share
With Live Share it is possible to share your Visual Studio experience and collaborate with your team members in a new way. For Visual Studio 2019 Live Share is fully integrated into the IDE making Live Share a seamless experience as well as making it very accessible to every Visual Studio user. Live Share let’s you work together on documents while keeping your own Visual Studio preferences and configuration. Because Live Share is a hosted solution (using Azure Services as a relay) you can, for instance, collaborate with a team member that uses Visual Studio for Mac when you are using Windows.

Image by Microsoft
Release Date
The release of Visual Studio 2019 for production purposes is estimated to be in late Q1 or Q2 of 2019. Release timing depends on the speed of development and testing and albeit it a relatively minor update from Visual Studio 2017, the preview is regularly followed by Release Candidate-versions prior to the release for General Availability.