Windows 10 comes out today. The early rumors were things like, “The START button is back,” and “It’s going to look like Windows 7.” Not.
Microsoft (and others) seem committed to the “flat” interface without the 3d buttons, and with limited shadows. It does look “cleaner” to me, but I’m not sure that translates to “easier to use.”

Bucharest Romania – June17 2015: Photo of Windows 10 Insider preview running on a pc screen with the new Edge browser. Windows 10 is the new version of Windows OS; it is set for release on July 29 2015.
The big question in my world is, “Will my (fill in blank with name and version of ERP system) work with Windows 10?” The only safe way to answer this question is to get the “official” answer from your ERP provider. Software providers will (eventually) release compatibility upgrades, and you can expect to see some compatibility updates within a few weeks for supported products.
The question becomes more complex when you ask it about products that the software vendor isn’t committed to supporting. Things like old versions of the software.
Being an IT consultant, I once told clients, “We’ll have to try it, there’s no official statement from the vendor.” I found out through experience that the best possible case was that it didn’t work quickly. The worst possible case was when the software appeared to work until weeks or months later when we discovered that a critical feature didn’t work. I’ve never personally lost data because of this, but I know of situations when this happened.
Microsoft initially announced that VB6 applications would not work on Windows 10. Some have termed this a looming crisis. It may be. Other vendors like Sage are hedging on the future of their products, with their statement about MAS 500’s lifetime. On the one hand they pledge support through 2020…on the other hand, they promise migration tools to other Sage products. Some information seems to be that VB6 is supported by Windows 10.
I think the net result is that most things that run under Windows 8 and 8.1 are likely to run under Windows 10…but I wouldn’t hang my hat on it until you hear from your vendor. There are also products out there that will break on Windows 10. At any rate, if you’re still using a DOS application…I’m not sure what to say.