I think pickups are worse then adrenaline personally. Both are blatent positive feedback loops. I do like the lack of predictability of adren though. If you wanted to lean more towards pickups for it, I'd rather just see big pills on the bases, so that when you got enough adren for a "power up" you got to choose which one you wanted, or choose not to burn it at all. Only being able to use one at a time would as well help the huge stacking that can happen.
Only problem would be how maps are authored sometimes around items, and what items are where make a huge difference.
It might aslo make it more interesting if adren was given as much or more, for damage recieved, as opposed to given. Or even making it more damage based, then kill based would help. In situations where you are out armored, and can do more damage then you can recieve, then you should get more adrenaline. Thus mildly countering armor's effects.
Only problem would be how maps are authored sometimes around items, and what items are where make a huge difference.
It might aslo make it more interesting if adren was given as much or more, for damage recieved, as opposed to given. Or even making it more damage based, then kill based would help. In situations where you are out armored, and can do more damage then you can recieve, then you should get more adrenaline. Thus mildly countering armor's effects.