2011 changed the face of warhammer 40k with very few releases. Early in the year we were still on a high from the release of the Dark Eldar. That lasted until Grey Knights hit. then wow, the face of 40k changed. Every marine player I know that was not painted were suddenly painted grey.
That lasted until the big let down of a White Dwarf codex release. Now I will be the first to tell you that many people are not impressed with this, but I know some extremly good players that took this codex and ran with it. Some powerful lists were hitting the tabletop, but with little fanfare.
Somewhere in there we saw some major FAQ updates. Deathwing and Black Templar were suddenly on the tabletops again.
Finally Necrons are making a splash. While they have not yet altered the landscape, it is only because we are still waiting for a Necron FAQ which we expect very soon.
2012 The Year of 40k
Here is where the excitement comes in. 2011 was a year of Warhammer Fantasy, and 2012 looks to be 40k heavy. The biggest event of course will be 6th edition, which is rumored to hit the shelves in July. Before that, we have possibly the Black Templar and/or Tau followed by the new codex Chaos Legions, which is expected either right before or after 6th edition. What a game changer that will be. Even Eldar are rumored to be the last codex of the year.