Themes
This blog post: http://jfnlinuxproject.blogspot.com.au/2015/01/windows-10-theme.html has a list of links and screenshots that show a themed desktop that looks roughly like Windows 10. This does need more work. But I am sure that you could make a Linux desktop resemble Windows 10 if you so wished. In time, there will be an actual Windows 10 theme pack for the Gnome and Unity desktops that make them look just like the new Microsoft operating system. Give it time.
The Numix theme is a nice alternative in the meantime.
Get this here: http://www.noobslab.com/2014/05/numix-theme-for-ubuntulinux-mintother.html.
Actually, this is a good Windows 10 theme for Linux: http://suyangt.deviantart.com/art/Windows-10-theme-for-Linux-Mint-Mate-541952193. I will have to give this a go and see how well it really looks. But give this a try anyway, this should make your Linux desktop look just like Windows 10.
Wallpapers
Windows 10 Blue wallpaper: http://microsoft-news.com/wp-content/uploads/2015/06/Windows_10_Hero.png. 1920×1080 pixels.
Windows 10 Snowy Hills wallpaper: http://www.hdwallpapers.in/walls/snow_mountains_windows_10-wide.jpg. 2560×1600 pixels.
Far Cry 4 mountains wallpaper: http://img1.goodfon.su/original/1680×1050/1/90/far-cry-4-vap-vap-v-p-vapvap.jpg.
Windows `95 default wallpaper, 9999 pixels wide! http://i.imgur.com/nE0IPhf.jpg.
Windows `98 wallpaper in HD: http://hdwallpapers.cat/windows_98_hd_microsoft_solid_blue_hd-wallpaper-1379994/.