Objectivity is basically impossible, granted, however the thread title is "worst game" so people could at least try.
As I said above (edited post) very few truly bad games exist, excluding things like move tie ins because I don't think they count due to the way they are developed i.e on the cheap with no effort, however we can broaden that to account for personal opinion without listing games which quite clearly are not in any way bad but people just didn't like.
I mean people listing games like Bioshock, Far Cry 2 or even BF3, these are games which many people didn't like, which I accept completely, but worst game they've ever played? No, sorry that is just absurd.
Comparing it to films, I despise the Fast and Furious series, however I can't realistically call them all "bad" films because they obviously offer something which justifies their existence or people wouldn't be watching them and paying for sequels.
While I wouldn't agree with those games listed I could see why some people may list them if their range of games played isn't very big.
As I originally said it's personal anyway, you can't be right or wrong here when the title is Worst game YOU have ever played?