Try saying that to a long-term user and see their horrified reaction.
I agree about multiple signatures - I have requested this on the Opera support forum. HTML stationery will probably come about when they implement HTML for composing new emails.
I would agree with the first point, maybe the second, but not the third. Does Outlook have an anti-spam feature that learns as you go on? Can it block malicious code in emails? These are all things worth considering. I made a move to Opera for email because I was getting too much spam in my Inbox with Outlook Express.
The main problem Opera's system has is the perceived lack of folders. To the new user, they want it just like any other email program - but it is not. It's a learning curve because it's more powerful. So instead of folders you have filters. All your mail is in one place (making it damn fast to sort and search, and easy to archive). You can still set up 'folders' but they are really 'views'. So all the spam is in one view (filtered automatically as it arrives), mail to individuals gets filtered into other views, and so on.
Aren't they all? Unless HTML stationery is the must-have feature, I'd say most major email programs have the same basic functions, because that's all you need. What's good about Opera's is the potential to go further. For example, the way RSS feeds are processed just like emails. No doubt they will add support for Atom feeds later. Will Outlook be updated? Well Microsoft have stopped upgrading any free versions of Outlook. You'll have to buy Windows Longhorn to get any new features. Meanwhile - just watch Opera fly.