With 299 they've over tripled the amount of Muds in the game. This means that they, potentially, could have over tripled the size of the game (they almost certainly haven't though.) and so they must've made the game at least a bit bigger, with new levels, etc, I'd say.
I'd guess this would be in new secret levels but I also think they've probably added new not-secret levels as well in which this comes to effect. (Either that or they must've added a load of new secret levels. :P ) And, of course, the rest will, presumably, be added to areas where Mudokons already are, as, as previously mentioned, Abe can now say 'all a ya'.
EDIT:
Also the thing about this not being a spoiler is actually a good point, really.
In the 'Spoiler Sticky' post Nate has said.
But this is not beyond a trailer is it? The 299 was
in the trailer? :P