Oh No! is available in two versions, one a stand-alone and the other an add-on disk that requires the original Lemmings. There are 100 new screens to solve and they have the same range of difficulty as the originals. Overall, these new levels are even better than the first set. I think that's probably because the designers have had more time to create them and have also had a year's worth of feedback from players. At any rate, if you're a Lemmings fan, Oh No! is an absolute requirement for your collection.