It's quite possibly my favorite Fury ability (yes, even more so than Titan's Grip, which I am currently back in love with - I know you were all pulling for us crazy kids to make it) just for the fun of hearing the swoosh-bang on a BT crit. That sound means hit the slam button for extra damage! It's like getting all cherries on the slot machine, but without having to sit with all those people feeding quarters into the boxes with that desperate, hardened stare. Those folks scare me. I get the sense they'd like an instant cast slam as well, so as to easily steal my quarters.
Bloodsurge has a few minor quibbles: the short duration of the buff after the bloodthirst crit means you have to pay attention and hit slam as soon as possible, and with the GCD and rage issues being what they are, it is possible to miss out on a slam for one reason or another. I generally don't find rage to be that big a problem with fury at this point (my fury warrior on Beta is but level 73, though). Also, while fury has Rampage to help with crit synergy, Bloodsurge is still an ability at the mercy of the RNG: if you don't crit on that Bloodthirst then you won't be using Slam for another six seconds. This is also not that horrible a setback, to be honest, but it is there.
Also, man, it's annoying when you kill a mob with a crit bloodthirst and there's nothing around to slam.
Bloodsurge rewards attentive play. If you're sitting back and pushing your rotation while eating a sandwich, Bloodsurge isn't going to help you digest, because the swoosh-bang going off will make you scramble to hit the keybinding for slam. It seems to be an ability designed to make fury more interactive and so far, I'm really enjoying it. I'd probably extend the cooldown by one second: I don't want to remove the hit slam now feeling of the ability, but I do want to make the GCD less likely to lock out a slam on me.
With Bloodsurge in fury, it made sense to move Improved Slam to arms. You're not going to miss this talent if you're fury, and if you have it, a .5 second slam doesn't matter: you're going to do instant slams and those points are going elsewhere anyway. IS was part of the arms rotation as it stood, so this move helps both specs.