Update - possible workaround: Restart Steam before launching CS:GO. It doesn't always work, but the failure rate is more towards 50% than 100%.
At the moment Counter-Strike: Global Offensive is sporadically (un)playable due to server issues. I'd be willing to cut Valve some more slack on this were it not for the fact it's been broken for about the last 7 or 8 weeks.
What happens is you try to join a game, then spend about two minutes staring at your screen while nothing happens. If you open the console up, it's full of messages like
CSysSessionClient: Unable to get session information from host CSysSessionClient: Cannot join lobby, response 5!
Then eventually we get the very helpful error message:
Failed to create session. Please check your connection and try again
Something's gone wrong, better blame the user!
If you are persistent enough you usually can get into a game, but there's a good chance it'll be empty.
Like I said, it's been like this for weeks. It's not just me, the CS:GO forums and subreddit are littered with complaints, although it may be 'localised' to Europe.
Valve (or at least, a Valve employee) eventually, after 5 or 6 weeks of continued problems, responded to this on an obscure mailing list:
The issue with sessions has been becoming a real problem with the growth of CS:GO user base. We are aware of the issue and are working on changing the core systems to scale better with the size of CS:GO community. Unfortunately this is not a quick rewrite, and there isn't an easy workaround that we can offer at the moment. We'll be sure to include a release note when the update resolving session issues is ready, but don't have an exact date to announce yet.
but this is a bit ridiculous. Scaling issues don't suddenly happen unless you have sudden unexpected growth (which CS hasn't); they are forseeable far in advance of becoming fatal problems. The idea that the matchmaking system is so complicated that it requires weeks/months of work to fix also seems questionable, and even if that were true, you could fix it in the short term by just throwing hardware resources at the problem.
If you're thinking of buying CS:GO, don't.