Markakis has definitely regressed, but I suspect he'll have a bounceback year this year if Miggy or Jones plays a full year behind him.
The thing about Markakis though is his completeness as a player. When you watch him, he's just so calm and patient at the plate and he's highly underrated in the OF, routinely leading/at the top of the league in OF assists. I'm not saying he's HOF material, but he'll eventually be a perennial all-star throughout this career.