Putin's always seemed so... collected. But he's acting downright irrational, methinks.
Sure, he got Crimea. But at what cost? The last time Yanukovych was ousted (Orange Revolution), the Ukrainians ended up making a mess of things and ultimately placing Yanukovych back in power. If Putin thinks that the Ukraine should be an integral part of Russia (and they do have quite a bit of shared heritage), he should be covertly sabotaging the new regime in Kiev, exploiting the divisions between the factions and letting people see the pro-Western faction fail yet again. Along the way, he could've also used this opportunity to replace Yanukovych with someone more competent. You know, doing things with a bit more finesse.
Yet, instead of acting like a former KGB officer, he loses his temper and acts like a cowboy. So he gets Crimea. And in the process, he shoves Ukraine straight into the arms of the EU/NATO. Oh, and Europe has become more united and determined to rein him in. Good job.
He's also underestimating the power of sanctions. Remember how Russia was virtually bankrupt and the economy was in shambles during the Yeltsin years? Putin took over, turned things around, and that's why he's popular. Except that the turnaround was based almost entirely on riches flowing in from the energy sector (so it wasn't really Putin's doing, but rather that of the world energy market), and Europe's his main customer. This would also hurt Europe, of course, but not nearly as much as it would hurt Russia.