No, it definitely isn't. I'm a software engineer and I've used it as my primary desktop OS for years. A year ago I went and paid $300 for a windows 8.1 box and migrated my whole system back to windows. There were just too many problems that got in the way of my work, things breaking after updates, graphics and printer driver issues, etc. I was spending more time debugging that stuff than a windows license costs. I don't like windows, especially windows 8, but it's stable. I did have to buy a start menu add-on, because Microsoft lost their mind with windows 8. I keep my Ubuntu machines in a VM now, where I can easily back them up, roll them back, or throw them away without affecting my productivity. It's not quite as fluid running an Ubuntu desktop at 4K inside a VM, but still quite usable.
If it's not ready for a seasoned software engineer, it's definitely not ready for my mom.