Sweden has formally joined NATO as the 32nd member of the transatlantic military alliance, ending decades of post-World War II neutrality and centuries of broader non-alignment.
Good for NATO, good for Sweden, good for Europe, good for Ukraine, probably good for the Russian people. Bad for specifically Vladimir Putin.
NATO is basically a mutual-defense treaty: all member states agree to fight on behalf of other members if attacked by a third party. Having Sweden in the organization means that there are more soldiers available if other members are attacked (good for NATO), it means that Sweden has allies if they're attacked (good for Sweden), and it means that Europe is more united as a defensible whole (good for Europe). And it reduces the possible targets for Putin's aggression (probably good for the Russian people, definitely bad for Putin). It also means that, once the war in Ukraine ends and they join NATO, they essentially cannot be attacked by Russia again (good for Ukraine).