It's an incredibly complex situation with it's modern history dating as far back as the Bolshevik Revolution and a major player being the exchange of Crimea from the USSR to Ukraine in 1954 by Khrushchev. Ukraine hasn't had a stable government since the dissolution of the USSR and Yanukovych was seen as corrupt/a Russian puppet by pro-Western and EU Ukrainians. I wouldn't say it descended in to Civil War, there was no militant uprising that resulted in the new government though there was a bit of violence and conflict in the protests leading up to the sacking of the government.

At the same time you can find evidence of Turkish and other Western involvement that has resulted in current situation and I'm still not sure what to make of that.

It could definitely be seen as a power grab by Putin. Crimea has historically been pro-Russian and some Crimeans feel as though they were given away to Ukraine without their consent. Putin might be looking to claiming the territory, or at least allowing for a semi-autonomous state to exist there. The latter might inspire the rest of Eastern Ukraine to follow suit, which would cripple the remainder of the country as the economic centers are largely in the East.

This is pretty reminiscent of the Georgian conflict and South Ossetia, as mk and amranu have already mentioned.