To Russia, Ukraine is special because it's a huge population of industrialized European territory. Russia has actually been facing a major population crisis for quite some time now, especially when it comes to working age men, and annexing Ukraine would add to their numbers by about a quarter, and secure control of one of the biggest exporters of grain around the world as well as consolidating the supremacy of Russian oil exports through the Black Sea. It would a also settle a feud that Putin has had personally with Ukraine since he first came to power in 1999 when they were a major source of rebuke and dissent.
To us, Ukraine is a major trading partner and a strategic ally. They're a former Soviet block trying to build a post-Cold War success story. But they also represent a domino in a bigger picture: if Ukraine falls to Putin's brand of politics, then his playbook could start exporting around the world. Territorial disputes everywhere could start following his pattern - Taiwan, Iran, India, and on and on. On the flip side, though, by protecting Ukraine, we have a unique opportunity to bring new allies against rogue nations; for the first time in hundreds of years, Finland feels secure enough to ally closer with the West - a disaster for Russian strategy because of its proximity to Archangel, their only port to the Atlantic.
In other words, there's actually quite a long list of reasons why Ukraine is special. But the thing is, even if it weren't, even if they were a completely generic country with no historical features, most people are anxious that this revival of pre-World War 1 Imperialist irredentism is a return to the old ways of doing things where you could start a war for almost no justification at all. Most people want to see a clear message that this kind of war is a bad move for the attackers as much as for the defenders. And that is pretty special all in itself.