Nemesis introduces two new abilities to our favorite game:

Laccolith creatures are creatures with a sort of "super first strike". They get to deal their combat damage to whatever creature they want, as soon as they become blocked.

Fading is definitely the coolest new ability that Nemesis brings to the table. A permanent with Fading is usually a lot cheaper than is should be, but it only stays around for a few turns. Case in point is Blastoderm Buy. This 5/5 mammoth can't be the target of spells or abilities which already makes him a threat, but add in the fact that he only costs 4 mana, and you've got an insanely powerful creature that will be in every green creature deck.

Nemesis also has five enchantments (one for each color) that have the same effects as some core spells, but can be delayed and used whenever you want. For example, Seal of Cleansing Buy allows you to play a Disenchant Buy on turn two, but not actually use it until later in the game.

Notable Cards
Even though it's only a common, Blastoderm Buy has proven to be a very powerful creature threat, and Saproling Burst Buy isn't bad either for that matter. Blue decks got a pretty good common as well. Accumulated Knowledge Buy is a cheap, but very effective card drawing engine.