Are you talking about the full Office Outlook, or the Metro ‘Mail’ app in 8.1?
The latter is very basic and really only makes sense for use with touch on a tablet. It does make it easier for a quick check on mail though.
Full desktop Outlook is the same as it is on any other version of Windows, except running on 8.1 you also get touch support enabled (can be turned off).
Full Outlook is OTT for many, but for me it’s the king of mail apps still, especially when connected to an Exchange or Office 365 server. Really liking the fancy stuff (in the business world) where someone sends you a mail proposing a meeting at a particular time or suggests some action to be done, and it automatically has parsed the mail and suggests adding tasks or calendar items for these.
However I will admit Outlook is not the easiest of software to configure mail accounts with.
Gmail I hate. Awful design, hate the way it does folders, generally impossible to use keyboard to make mass selections and deletions. Largely online only also. Also I believe you can’t on the free version use it to access (without importing as a copy) external IMAP mailboxes, only POP3. You can however use a client app to access Gmail using IMAP.
Thunderbird is nearest I got to Outlook but even today it can’t do calendar built in and the optional add-ins were poor when I tried them compared to Outlook.