What has Russia gained? In material terms, I'm not sure. Raedwald suggests "the industry and the wealth producing bits, whilst Kiev has the beet fields and the pensioners" and if that's true, it's more than just a bit of swagger and nose-thumbing on Putin's part. But I've also read that the Crimea and these eastern parts are going to cost him a lot of hard currency to keep them happy. So it's a rather costly macho gesture ? Or (as some say) a price well worth paying to fend off an existential threat ? - at least, as perceived in the Kremlin.
The latter seems an extreme assessment. All in all, I'm inclined to think it's a rather unusual (for the 21st C) example of best-form-of-defence-is-attack. The lazy neocon strategy of baiting Russia along its borders, not to mention the expansionism of the EU (and NATO), provides plenty of motive for Putin to flex his BM 21s. He has followed Soviet doctrine pretty much to the letter (albeit on pinprick scale), as I confidently predicted here. There's also an element of making the best of a bad job, as the Ukrainian separatists are probably not 100% under control - or at least, they weren't when this whole thing seriosuly kicked off. A bit like China and N.Korea (again, on a tiny scale): why do the Chinese indulge the childish bastards ? - well, they are their childish bastards, so piss off the rest of you. Maybe now Putin can get back to the serious business of managing an economy around $50 oil, which he very much needs to do.
There is one good aspect to this. It will be ten times harder for Russia to play its 'little green men' trick again in (say) the Baltic - tactically, that is, not logistically - because we've seen it now. And perhaps the Typhoons weren't such a bad investment after all; so long as we keep up the NATO spending now. But with the Greek thing simmering away, that might be another story.