What makes the Ruy Lopez opening good?


riversadowsky wrote:
Well, here’s the thing. The difference between these this position:
And this position:
Is for all intents and purposes nonexistent. The bishop is still x-raying the knight and the king, temporarily stopping Black from playing d6 or d5, but if Black plays b5, suddenly White is playing an Italian except with an extra target on b5 to attack with an eventual a4. So what makes the Ruy Lopez good is that you can think of it as a “better” Italian.

Yes, there's a lot you're missing :-)
Bb5 is a continuation of the attack on the black pawn on e5. Therefore, BxN is a natural follow-up. Unfortunately, for tactical reasons, it doesn't win the e-pawn (try to figure out why yourself). But it can be played, as White gives Black a double pawn and creates an unbalanced position.
Even better is Ba4, and as others have already pointed out, Black hasn't gained any tempo since a6 is not a development move. To cover e5, Black must later play b5 and White gets new attacking points after Bb3.