If you've just installed Yosemite OS X 10.10 then it's worth having a look at this collection of features.
Every new release has several new features and Yosemite is no different. The Mac's looks have changed since the last iteration, Mavericks 10.9 and you will either like it or not, I do! It's a bit like the iOS version 8 which polarised people with it's new 'open' look. Yosemite is similar.
I have found it a bit better than Mavericks and I like it. But make sure that you have enough RAM before installing, specially on older machines by which I mean more than 2 years old. Older processors and new operating systems mean more RAM!