Here's another account:
http://forums.caves.org/viewtopic.php?f=8&t=15722&sid=7f8ed2758e90b9e9f8fe85ecb925e78dA few notes.
The room that was discovered measures approximately 100 feet in diameter, but may be smaller than the Grand Ballroom, which I believe was discovered in the early 70's. This is likely the "largest room" discovered in Carlsbad Cavern in many years, but it would be very premature to call in the "biggest discovery".
The area being explored is in Spirit World, a discovery originally made in 1985 by Kerbo, Goodbar, et.al. The original Spirit World discovery included roughly 1,000 feet of surveyed passage, but exploration of Halloween Hall will add to that total.
Chocolate High was explored in the early 90's, is certainly a larger discovery, and includes a couple of miles of passage, though no large rooms.
DB at the base of the climb made on Halloween in Spirit World
ST in Spirit World after making the discovery
A decaying bat with some of the bat bones in Halloween Hall