At work or Academia, I had used all there is to use. DOS, Windows, Solaris, HP-UX, Sinix, VMS, Linux, FreeBSD...
At home, it was DOS (3.2, 3.3, 5.0, 6.22) Windows (WFW 3.11, 95, 98, NT4, 2000, XP, Vista) all the way (with a brief innuendo with Warp), until Early 2009, when I declared my switchover to MAC Successful.
Now, Apple forced my hand by not releasing Win7 Drivers for the 2015 13"Air... So, between having a ragtag fleet of machines on Win732, Win764 and Win8.1 64, I'll go 10 all the way.
The fact that I can get Windows 10 Working on a Toshiba Satellite A123 ** (My last windows machine), with an Xpress200m Chipset whose graphics part is based on a chip (R300) released in Aug. 2002, and a processor whose architecture (Yonah T2080) was released on 2006 speaks volumes at the effort microsoft has put in preserving compatibility AND make the OS perform better.
On the same resources, Win 8 will perform better than 7 and Win 10 will outperform them both. It has actually breathed new life into the old machine.
What really interest me is the new powers under the hood. Better performance (as said before), Edge, better included antivirus and security tools, DX12, etc, etc, etc.
Maybe things moved around a lot from what I remember, but is in no way as bad as windows 8, were I had to rip of the virtual machine due to the hotcorners, and wanted to pull my hair everytime I had to use a Win8 machine from a friend without a shell replacement. Besides, if one does not like the interface, one can change it (as they said in the TFA, Classic Shell works like a charm, and I am sure there will be other customization apps in no time), if they removed mediaplayer, there is MithTV or VLC, the app store is empty, so what, is not like I forgot how to download an exe or a msi file...
But then again, I use this only for some games (currently Batman Arkam Origins, and anything that strikes my fancy that Steam has not ported to Apple yet) on bootcamp, and via VirtualBox on raw partition for Visio and Project.
The fact that the upgrade is free sweetens and seals the deal (if I had to pay for it, or had to go through the hoops of the university to get the license key, well....). Yes, there are privacy concerns, and I will deal with them, the same way I dealt with iCloud and all of Apple's privacy invasions, I have the knowledge to do so, and I can relay on my fellow techies when my knowledge fails me.
For me is a welcome upgrade, one that will bring homogeneity to my fleet, along with better performance accross the board, and I am recommending all non-techie friends to upgrade (after updating FW, maxing RAM and putting an SSD, of course), especially from Windows XP. Besides, I already issued them a stern Warning. After march 2016, I'll only answer questions about Win10 or "El Capitan". That will drastically cut the amount of free tech support I must do... ;-)
Welcome Windows 10, you may not warrant a rolling stones theme song, but your low-key entry will make many lives easier...
Suerte a todos y feliz dia.
** Yes, after firmware updates, maxed RAM to 2GB, and put a SATA3 64GB SSD on the puny SATA1 interface of the Xpress200M
PS: For what is worth, I have CrunchBang++ for basic Linux demos to my students in the Toshiba (the machine I carry around in mass transport to class, because, if they mug me, I'll not miss it), and have A few CentOS and Oracle Linux machines for, you know, stuff...