Short deck, or 6+, is what they call it.
I played in a short deck MTT on ACR back in October. It was pretty fun. It is a little different with the 2s-5s removed, but not different enough to be too difficult to just jump right in after learning the differences in hand ranks.
The rank in
hands changes because of the
odds changing when the low cards are removed. So, A flush beats a full house, and three of a kind beats a straight. Also, the low straight is now A-6-7-8-9
Other than that, its the same game. Your strategy and playing might change a little because most of the hands played will now be bigger hands facing bigger hands. Oh, and having suited cards doesn't matter as much when entering a hand.
If you want to try it out, I suggested watching a table play it for a while first. It will give you a much better idea of the differences.