I chose this card over the similar priced HD6770 because that card requires a power connection to the PSU whereas this 6670 gets all its power from the motherboard. While clearly the 6770 would have better performance than this 6670, I was pleasantly surprised by what the 6670 could do.
Installation was incredibly easy, I just unplugged my HD6450 card, plugged in the new card and then ran the driver cd. Had no problems at all. The Asus driver disk also comes with a handy piece of software to show the card's performance and temperature and allows overclocking (although I have not needed to do this).
My primary reason for upgrading was to run Skyrim which was unplayable on my old card. Now I can play on low~medium settings at >30 fps which is exactly what I wanted. Crysis also runs perfectly on High settings and I can now play Payday the Heist and Bulletstorm on low settings which I couldn't do before.
Card so far is running cool and quiet, can't hear it at all over the sound of the rest of my fans etc. After a few hours of Skyrim, temperatures were only in the high 50s. Highest I have seen it go was 61 degrees. Compared to my passively cooled HD6450, this is a huge improvement.
All in all, if you are looking to play the latest games, this card will handle low settings at a decent resolution. It is certainly worth considering if you are not obsessed with having the best possible graphics, I know I would rather be able to experience Skyrim on low graphics than not play it at all! For older games, this card will easily max out all the settings. For the gamer with a tight budget and no PSU connector, this card is perfect.
Edit: Got Battlefield 3 today, runs flawlessly on low-medium settings :) Even more reason to recommend this card.