1 c4 e5 2 Nc3 Bb4
I guess 2...Bb4 is a sort of reversed Rossolimo where Black seeks to compromise White's structure, and can even benefit from not having played ...Nf6 because he can directly play ...f5. The down-side of not having...Nf6 is that White can play 3.Nd5:
I have chosen to focus exclusively on this move because I think it is critical, and because I know that if it wasn't for this move, I would certainly play 2...Bb4 myself. The interesting point now is that just when White thought he was setting the agenda, Black can choose to play 3...Ba5, 3...Bc5, 3...Bd6, 3...Be7 and 3...a5 and they are all playable! I would say that Be7 is probably best, followed by 3...Bc5 and 3...a5, with 3...Ba5 and 3...Bd6 being a little dubious, but good enough to try if you want to confuse your opponent as early as possible.
Reflecting on Aronian - Shirov got me thinking about this line because Black drew so comfortably with 3...Be7:
I have also noticed that England's rising star, David Howell, has played this move, and indeed I watched some of Speelman - Howell live. A little analysis on these two games makes me feel that after 3...Be7 White should probably play 4.d4 d6 but I prefer 5.Nf3 to 5.e4 and I think White has reasonable chances to be better, as long as he is not too ambitious.
I found 3...Bc5 difficult to get my head round, but my notes to Lautier - Kramnik hopefully sheds some light.
3...a5 is an open question, because there are just so many possibilities for both sides, but I suspect White should try to steer the position back to the other lines and in most cases it is really difficult to say what the inclusion of a3 and a5 makes:
I examine this question in Popov - Konavalov mainly because I was so impressed by the way White made the transition from opening to middlegame.
Salov - Kramnik featuring 3...Bd6 looks like a classic two bishop endgame grind, but I suspect White is better off keeping more tension in the position with Nd5-f4, as indicated in the notes.
Petursson - Sokolov was a very one-sided game, included as a reminder to subscribers not to try these lines without adequate preparation. 3...Ba5 is probably not very good, and again France's Joel Lautier again seems to show the way most convincingly.
Finally, for those who don't care about the above variation, I included a very recent game from Linares. Radjabov - Aronian shows why Black should hesitate to play ...c6 unless it is really necessary.
Till the next update. Jonathan