Once called feminist jungle, 2-Step evolved from speed garage, or house with basslines. The main difference between this and 2-Step is the use of more jungly beats that are not typically in the 4/4 time signature.
Although derived from house, 2-Step sounds a lot more like breakbeat. This is because 2-Step takes breakbeat's broken beat a step further by removing every second and fourth beat from house in simple tracks and by using irregular kick-drum patterns which syncopate with the bassline in more complicated ones. The result is really phat beats, but not at the excessive speed of jungle.
The other characteristic of 2-Step is the integration of all parts of the music together in a way that hasn't quite been done until now. Each element works as part of the rhythm, melody and texture. This philosophy is even applied to vocal samples, which until now have been divided from absolute electronic music. House, breaks, etc. often make use of sampled sound bites, but these tend to be layed over the music rather than integrated into it. 2-Step, on the other hand, uses vocal samples as part of the beat and melody as well as part of the texture. In order to fit human voices into mechanized, synthetic beats, vocal samples are often chopped into pieces and put back together again. Vocals are treated as just another part of the music. As such, they are also run through filters just as every other sound in electronic music.