There's nothing you can watch that will prepare you for Generations
. Up until 2009, it was the worst Star Trek movie.
Seriously though, you don't need to have seen any TNG before it really. It's self-contained unlike First Contact which has a backstory.
In the spirit of that "Most unjustly hated ep thread"
I loved Generations. The opening part is fantastic, I loved the soundtrack. Thought Stewart's acting in relation to what happens to his family was awesome.
Everything else was 'ok'. But I loved those parts.
"My God...was anyone in here?"
edit: You don't have to defend your hatred with a long list. I understand why peeps didn't like it.