I can't comment on most, since I don't have the originals.
However, their Against the Giants hack looks like a basement level has been added to the hill giant fort. Not 100% sure on this, but I've run the original, and when looking over the hack it was a case of, "hrm, I don't remember that."
I wouldn't call them slapstick. There are some silly bits in each one (I think a requirement of their deal with WotC), but if you want to run a "straight" game (D&D or Hackmaster), it's easy enough to just ignore the bits.
I think the hacks also flesh out the module quite a bit, in terms of discriptions and backstory. I'd page through one to get the feel for it.