I came from Windows, so the answer for me is: Yes. Very much so.
I've been using Windows for about 15 years now, so for me, Mountain Lion was a breath of fresh air. I've seen some people here say that they don't understand why people hate Windows so much after moving to Mac. For me, there are 3 reasons.
1. Integration. I love the way it integrates with my iPhone, iPad, and Apple TV. I love that iMessage and iCloud in general are now baked right into the OS, as my wife are daily iCloud users.
2. Maintenance. I don't feel like I really have to do any. I moved all my media backups over, set up Time Machine on an external drive, and within an hour or two, I was USING my new Mac, not setting it up or learning how to do stuff. I'm not running any 3rd party security software, and the OS is running like new 5 months after I first booted up. I cannot say the same thing for Windows. Even Windows 7 started running slower after a few months, and that's with me barely messing with it at all.
3. Ease of use. This kind of goes back to #2 I guess. I am very comfortable in Windows and know how to accomplish whatever needs to be done. But I feel like on OSX, I just fly through everything. It's less clunky, less cluttered, and more stable. I love the feeling of using my computer instead of tricking my computer into doing what I want it to do.
So needless to say, I am beyond pleased with Mountain Lion. I'm on a late 2012 model Mac Mini, and I'm 100% thrilled with it. I use it with our large HDTV as well as with my workstation I have set up at my desk when needed. I am still on my iPad or iPhone most of the time, but when I'm home and have the time, I still being on my full blown computer instead of a mobile device.