I just got Vista (with my old xp cd handy just in case), no problems so far. I became impatient and bought the Vista Darwinia to check out the new effects. They weren't as spectacular as I'd hoped. I've had some mouse trouble, it's not as sensitive and smooth as it was in the original. However, the xbox controller is nice. You can direct the squaddies with one stick will aim and shooting your lasers with the other, similar to games such as Geometry Wars and Bullet Candy.
As for the effects, the screen warping explosions are cool. However, when your camera is at the wrong angle and you're throwing volleys of grenades, sometimes the screenwarps can make it hard to see what you're doing.
I wasn't sure what soul 'auras' would be until I saw them. They're another screen warping effect around the souls that throbs out and in like heartbeat. And the reflections are nice, but nothing totally spectacular. Then again, if they went too overboard on the effects, they'd lose the 'retro' style of the game. Overall, I like it.
I'm curious if anyone has the same mouse trouble as me.
If anyone wants screens, I'd be happy to supply them.