The current philosophy in the NFL, as it relates to the draft, seems to be that in the first two rounds you can get NFL-ready players. I think in this year's draft, with more kids than ever playing football and coaching getting better at the high school and college levels, that was extended to the first three rounds. After that, you're looking for guys with flaws that you think you can fix. These guys may one day become good, or even great, but there's a chance they never amount to anything as well. These are called "Project Picks".
Looking through the first 2 rounds of pick for the Chargers in the past few seasons, you'll see names like Antoine Cason, Eric Weddle, Antonio Cromartie, Marcus McNeill, Shawne Merriman, Luis Castillo, Philip Rivers and Igor Olshansky. That's not all of them, but that's most of them. Each of these players had an impact in their rookie seasons, either as a starter or a backup, and (if they didn't already start as rookie) eventually forced the team's hand in getting rid of the incumbent to get them more time on the field. Cason's not there yet, but that's mostly due to the play of Cromartie and Quentin Jammer (another recent first rounder) rather than his own drawbacks.
So, in this year's draft, the Chargers went in with more holes than usual. There were holes along both lines, and the team needed to look for help at RB, LB and Safety. This was not the draft to be spending first-rounders or even third-rounders on "projects" that wouldn't see the field in year one. This was the time to find players that would make an immediate impact. How did the Chargers do?