Outlook is not. Been using Notes since 1999. Yes, the UI is clunky but it works and supports pretty much every platform out there with feature parity. We run our infrastructire on Linux, clients on Windows, Mac, and Linux and all have the exact same experience and feature parity. Can't say that for the garbage that is Outlook and Exchange!
You'll be saddened to learn that the company I work for (which employs ~100 thousand people around the world) has just dropped Notes for good. The end is coming, my friend!