On one hand this could be useful given for years Steam has seemingly insisted that "indie", "Family" and "Action" are useful genres. But on the other hand, it's probably going to take an age to actually work and it's once again another new feature on top of the burgeoning 2010 build of Steam.
Someone at Valve really needs to stop the feature creep and get Steam a major overhaul in usability, especially if they're going to continue adding games at the current accelerated pace.
Since the 2010 redesign they've added:
Greenlight
Tags
Steam OS
Big Picture Mode
Market
Workshop
Hubs
Steambook
Guide
Early Access
Linux
Recommendations
Reviews
Screenshots
Software
Probably others
And this is all built upon two websites, one a store for games, and the other a community feed.
Edit:
I'm not sure if this will work without like a billion people using the tag (from how it reads on the page) but:
http://store.steampowered.com/tag/en/PXOD/
If you tag games as "PXOD" that you recommend, potentially they'll end up on there.