The fact that it stalls gameplay and turns combat into a mess of CQB without intention of doing so. If I'm shooting somebody and they are one shot from dying, I do not want to see any more bullshit of them deploying an item or using an ability to escape from that death.
"you can still rush into it!" - not if I'm a decent ways away, only in close quarters and even then it causes a grenade/AR spray/melee mess.
The flip side to that is, you suckered that guy into dropping his bubble shield to protect himself rather than some other use for which it would be more beneficial. I loved seeing that in Halo 3.
Bubble shields work when they are scarce. I always got a kick out of seeing the other team have some bozo drop the bubble shield to save themselves when it was desperately needed to protect a flag carrier, for instance. Knowing theirs was out of commission was useful. As a tactical element I thought it was a good addition. The change in Reach where they can be destroyed pretty easily (especially with plasma weapons), combined with Halo 3's relative scarcity, is something I'd like to see.
The trick with that kind of equipment is always making sure it was deployed correctly. It shouldn't be in a FFA game, for instance, where its only use is the one you described. Personally I loved those little moments where combat would pause and we'd have to rethink what to do. But if you push that too far we get Reach.
I don't even know why we're arguing how to fix equipment. Equipment is worse than armor abilities. Hands down. There's no argument. I know you all hate armor lock but let's get real here.
I don't really see how this is the case. Dropping one loud beeping trip mine is not the same as some dude with evade and a sword on Countdown, which is game-breaking. One bubblle shield on a map is different than everyone spawning with a reusable one.
I liked equipment because they make things like trip mines and power drains possible, rather than focusing on player ability. Reach's mistake was forcing pick ups, equipment and armor abilities all to work the same way (that would be, as armor abilities). Different categories of abilities should be treated differently, and deployed with greater care than things like evade are.