I bought this before Christmas for £5.44. I wish I'd waited now!
Yes I know it's not the most up-to-date PC game but I'm playing it at the moment and have been pleasantly surprised. I recently finished ACIII and frankly didn't much care for it. I thought the graphics looked bad and it was very laborious to play. However AC Liberation looks lovely in 1080p and plays at a nice pace.
You will need a Ubisoft account to play this game. Most of the time Ubisoft is okay (accept right now when the servers for the whole of Europe are down!!).
Hope this helps someone. For £1.50, it's an easy buy...