Outlook as "features" is welcome, Outlook as slow, heavy, pen&touch unfriendly that doesn't work offline and doesn't receive notifications when doesn't actually run in background is not, simply they should have used native tech, but they're lazy as hell.
Outlook is the most powerful offline mail program on the planet by a wide margin. That I can say definitively. When I know that I won't have an Internet connection for several hours, I'll often make sure my traveling laptop has been on for a minute so I know that Outlook is sync'd for offline use, and it's all automatic in the background. Other than needing to be online to download and upload messages, there is nothing the user needs to do. But if you have a slow connection, the user can choose various partial download (headers only, first several lines, etc.) and upload options to work with those too. You can even specify the download order or specific folders if you don't have the bandwidth available to download everything. There is NOTHING in the same league as Outlook in terms of features and power, including especially for offline and various online speeds and latency configurations. The other criticisms are a mixed bag.
For pen, poor to fair. It does support Inking in messages, which is excellent (and arguably the most important component of Pen support, depending on your personal needs), but navigation with pen and filling in fields is no better than apps that don't support Pen at all (works like a mouse and uses the standard Ink handwriting boxes to fill in text).
For touch, it's... subjective?

I use it with touch daily. The only real problem for touch is that the touch points are fairly small, because it was not designed from the start specifically for touch, but it does make them larger for touch than for mouse and everything scrolls, zooms, etc. as you'd expect for multi-finger touch (even has a modified version of that nice stretch/bounce effect at the end of scrolling the list of messages, folders, calendars, etc.). It's OK, but not great. It is MUCH BETTER for touch than a program that is not at all designed for touch.