From ERA to FB/GB rate to OPS to BABIP, no sport is as driven by statistics as baseball. Furthermore, each stat category holds differing values based on the perspective of each fan.
Personally, for pitchers I look at their K/9 and WHIP as indicators of value. If a pitcher is missing bats while limiting hits and walks, then it follows that he should be successful.
Others may prefer a pitchers K:BB or WAR, but that's what makes baseball so compelling. Find a stat that you think proves a player's worth and another fan will find a stat that refutes it.
The following slides are a collection of stats that have jumped off the page for me as this season is unfolding. Some are disappointing, some encouraging, while others are just downright shocking.
I'm sure you have your own opinions on what stat has surprised this year, so please feel free to let me know in the comment section.