Demos are up on the US store.
Vanquish is pretty much exactly what I expected, the slomo works perfectly and it's not too overpowered because it shares an 'overheat bar' with your boosting and melee. The boss you get to fight loves to shoot missiles and lasers everywhere and you take it down in a fashion similar to Lost Planet. As far as I know you can only find four different weapons in the demo, an assault rifle, shotgun, heavy MG and a sniper rifle, but they're all completely different so there's plenty of variety for the 25 minutes or so it takes to finish the mission. There are also a couple of bipedal mech things and a few stationary turrets lying placed around the area so if you get bored of using normal guns that's another option. The one negative I want to point out is the inclusion of QTEs but there was only one instance of them and it worked well so I'll reserve judgement.
I'm buying this game.