Like Windows 10, the next version of Windows Server gets the Start menu back; initially it's very empty, but you can pin tiles to it.
Nested program groups open in place in the Start menu; this is back to the Windows 2008 way of working.
Server Manager isn't the way to do everything in Windows Server: tools like Hyper-V Manager and Failover Cluster Manager have lots of the new features, and they'll also be in System Center in the future. But if you want the full power of all the Windows Server features, get ready to learn PowerShell.
At the moment, Windows Server has all the Windows 10 client interface features, including virtual desktops triggered by the task switcher button that you can't remove from the taskbar. The good news is that both the command prompt and PowerShell window get the new Windows 10 console features like copy and paste.
Storage Replica is a block-level synchronous replication between any Windows volumes, from Storage Spaces to SANs over SMB 3, that you can drive from the Failover Cluster Manager or PowerShell (which becomes increasingly important for managing Windows Server in this version). You can use it to stretch a cluster over multiple locations for disaster recovery, but it's useful any time you need to replicate a volume. When you replicate to a volume, you can choose to wipe out the data that's already there or to reuse it. For a large disk you'd otherwise courier between locations, that can save a lot of time.
At the moment you have to use PowerShell to turn on the new storage QoS options. Instead of individually limiting the IOPs available to specific VMs, you can set limits for groups of VMs — or you can protect a certain amount of IOPs on a critical VM and Windows Server will take care of throttling all the other VMs to make sure the bandwidth is there. Next year, you'll be able to do that (and more) with policy and System Center.
RemoteFX adds support for DirectX 11 and OpenGL 4.4 with OpenCL 1.1 in Windows 10 VMs. You can also configure the way dedicated video memory is allocated instead of it being set automatically. That lets you use GPU-accelerated applications in VMs. This will work with more than the cards supported for RemoteFX in Windows Server 2012 R2, although it still has to be a passively cooled GPU because it's running in a server. So far Microsoft has tested this with Nvidia cards, but for launch both AMD and Intel integrated graphics will also be supported.
If you want to run GPU hardware-accelerated applications like Photoshop in VMs, so you can use hardware-accelerated filters and effects, you'll need a powerful GPU in the server. You'll also need to allocate 512MB-1GB of video memory. Microsoft is working with Adobe to make sure filters that use OpenGL acceleration will be supported, and is also working on support for hardware-accelerated Chrome. Not all applications recognise the virtual GPU yet, so this is something to test in the preview.
You also get an alternative to remote desktop: Windows MultiPoint Server is no longer just for schools and it will come as a role in Windows Server. It will let you connect multiple keyboards, mice and monitors directly or remotely to the server (using low-cost 'zero client' hardware) to run multiple desktops, without needing an RDS gateway or broker.
The 20-user limit for MultiPoint is gone, but you'll need multiple GPUs in your server as each supports two or three desktops, and you'll need RDS CALs (instead of specific MultiPoint CALs). This is interesting for lightweight users, which could be point-of-sale systems or basic office workers.
Snapshots are used as the basis of the new Hyper-V backup system, which you currently drive from PowerShell but will be supported by third-party backup tools. You can also take production snapshots using VSS. Snapshotting was only supported for development and test before, so this is a welcome recognition by Microsoft that many admins already use it on production systems.
You can now change the amount of memory available to a running VM manually, without having to make it dynamic.
When you take a snapshot or a backup of a VM and import it, you can choose to keep the same VM ID, rather than having Hyper-V throw it away and replace it. This makes it easier to reuse your scripts.