Granted, the O's were playing their fourth home game, squarely in the slow period after the rush to get out to the first series has worn off but before summer has arrived and the kids are out of school. They were also off to a 1-5 start (now 1-6), it was a Monday night and the Rays in town, who have a good team but few displaced fans in other cities. Still, with a solid young core like Baltimore has, you'd think it a few more people* would have made it out.
While Camden Yards is still the face of the "New Ballpark Movement", any novelty has long worn off. It doesn't seem like it, but the park is now hosting it's 18th season and is actually due for some renovations over the next year or two. As Craig notes, there are now only 10 parks older than Camden.
It's quite jarring to see the place so empty, but when the Yanks come to town at the end of the month, surely there will be fewer of those seats unoccupied.