The solution can be derived from the insights from here. I've performed the following steps for my Outlook 2010 32-bit and it works perfectly. I never investigated its compatibility with 64-bit Outlook, so please anyone who try it, share your experience. So let's begin:
Create a custom form by pasting the following code into text editor like Notepad:
Comment=Allows exposing last verb executed and last verb execution time in Outlook
DisplayName=Last Verb Exec Time
DisplayName=Last Verb Exec Type
(credits to www.codetwo.com)
Save as a file LastVerb.cfg or any other name of your choice with .cfg extension. Take care about Notepad that may save you file like LastVerb.cfg.txt and Windows would hide .txt extension. Rename it manually in such a case.
Find location of Office custom forms on your system, something like C:\Program Files (x86)\Microsoft Office\OfficeNN\FORMS\NNNN or C:\Program Files\Microsoft Office\OfficeNN\FORMS\NNNN. For example, on my system it is C:\Program Files (x86)\Microsoft Office\Office14\FORMS\1033.
Copy LastVerb.cfg into that location. On Windows Vista or 7 you will need to confirm administrative privileges (and of course, must have them) in order to put your file there.
Register this custom form with Outlook by going to menu File, then choose Options, Advanced, Custom Forms, Manage Forms, Install..., find your LastVerb.cfg file and click OK button then Close and again OK, OK.
Now you can use this custom form named LastVerb in several places in Outlook to set criteria for messages based on Replied / Forwarded status. For example, let's filter your Inbox view to see only unreplied (and unforwarded) messages. Go to Inbox folder.
Go to menu View, View Settings, then click Filter..., choose tab Advanced, click button Field
(You need to perform this step only for the first time.) In drop-down list click Forms..., then in top-left corner choose Personal Forms from the list, click on LastVerb item in the left panel and then button Add ->. Click Close button.
Click button Field again. This time, in the drop-down list find and click LastVerb then finally, Last Verb Exec Type. In the middle-bottom box titled Condition, choose does not exist then click Add to list button. Click buttons OK twice to confirm and close all dialog boxes. Enjoy unanswered-only view! Though I personally prefer using Conditional Formatting... in View Settings and paint unanswered messages into some really visible colour.
Phew, finally. Nine really sophisticated steps to achieve some really basic functionality - Microsoft ways, I guess?..