The first time I tried to log in today, it got to the game and then lagged out as my character was logging in (I downloaded it via steam on this computer)

The second time, Steam popped up a note saying it needed to convert content to a more efficient format (weird, never saw that before) when it was done, it then said it needed to download "Missing content" (remember, 30 seconds earlier, it got all the way into the game and only lagged out, with no "missing content" warnings) - Now it's apparently downloading something pretty huge (Been half an hour, and it's only 3% complete)

So what's with Steam compressing content, anyone more familiar with steam know what that's all about?

And did some big update just get put up in the last half hour?