What do you like about your favorite OS, and what do you dislike about it?

So, I’ve had some ideas on what I’d like to see in my ideal OS, but I’d like to see what others think.

Now, I could just say, “what do you want in your dream OS,” and someone would certainly suggest various things that haven’t been done – which is a good thing. But, we live in the real world, and we use OSes that exist, and have been proven to work (or not work, as the case may be.) So, what’s your favorite OS, what do you like about it, and what do you dislike about it? In other words, if someone were to make a new OS inspired by your favorite OS, characteristics would you want them to keep, and what would you want them to change (and how would you have them change it?)

Please refrain from flaming others for their OS choices, or their reasons for liking or disliking an OS. Offending comments will be edited out. 🙂