Why didn't Russia get bogged down in Crimea? Without outside involvement, I see no scenario where Ukraine is able to mount a meaningful resistance, either militarily or in a popular uprising. They failed in 2014 and the situation is worse for them today.
The two most likely options I see:
1. Russia invades and overthrows the current regime. Mass arrests of far right militia and anti Russian elements in Ukraine. Installation of a pro-Russian Belarus like regime. The perpetrators of the Odessa massacre get special treatment. A largely bloodless and quick war.
2. Ukraine agrees to all of Russian demands at the least minute including recognition of Crimea/Donbass and pledges not to join NATO.
The only hope for Ukraine would be the imposition of a no-fly zone over western Ukraine if conflict breaks out. However NATO have so far shown ZERO intention to get militarily involved in this conflict.
I'll argue 2014 was a massive Russian failure because they achieved very little.
Was it in hindsight they couldn't leverage the frozen conflict into a lasting diplomatic breakthrough? Partially but the writing was on the wall.
Crimea was special because they were always 90%+ pro Russian and we saw mass defections to the Russian side in the military and government. Nowhere else except parts of Donetsk and Luhansk, either because of apathy, fear of unrest, or the Russians got the numbers wrong on Russian sympathizers.
Putin must regret not going in hard at the start of the Euromaiden.
He was risk-adverse then because of the failed uprising, but now it's backs to the wall.