When I bought Far Cry 2 off of D2D about a year ago I immediately tried to throw the key into Steam an not surprisingly it didn't work.
It's cool that at least some games do.
I grabbed one of these Amazon cables for about $3 a couple months ago after the $20 LG one(from Target) I had took a dump and shorted out. It's been working perfectly fine.
It's pretty fun for a while at least. I bought Trouble in Paradise when it came out because I had played the first for about an hour. The best way to describe it is that you're farming the Pinatas and trying to make/lure bigger and better pinatas to your garden.