It was the single-player that made the game great, and it would be wonderful to see more levels of the quality and difficulty of those found in the original. If they can tie them into the films more closely as well, it would be tremendous. Top stuff all round. Here in the UK, multi-player has yet to take off in the same way it has in the States. We don't need new weapons - the Predator is confusing enough as it is, with too many weapons to choose from.
Most people seem to stick with the disc and the shoulder cannon anyway.
For the multi-player arena, what the game most needs is new maps, and a level editor. But finally, and most critically, I would like to know what form the expansion will take. Don't rip off the fans. I completely agree with you. As for how the expansion should not have new weapons, I don't agree with you.