@Vesper, the mega campaign is a promised future download (and CA is pretty reliable on this) with a future date some months (at least) in the future. So don’t worry about the mega-campaign for now.
You should be able to find WH2 at a discount, perhaps at a Spring Sale or the equivalent. WH2, even at say $30 is well worth the money, even now. I enjoy the Vortex Campaign, and the combo campaign of WH1 & WH2 is excellent. IMO, you can pick and choose on the many WH2 DLC - some are good, some are just frosting on the cake. The core 4 races that come with WH2 will provide many hours of play. The High Elves are pretty standard but with dragons (!), the Dark Elves are evil and a bit micro-heavy but many players love them, the Lizardmen are the stoutest of the stout, with dinosaurs (!!) although hard to play well due to lack of mobility, and the rat dudes, well some love em. They are arguably the most crazy and fun faction in all of WH thus far, but I find them annoying.
I have some old AARs on here somewhere featuring High Elf vs various races action and that will give you a good taste of why WH2 is good. Let me see if I can find them…