I'd agree that Furious Power and its mirror on Sentinel are somewhat underwhelming. While I do feel that there's a place in game for these sort of "Press X ability to buff your next Y ability", the nature of Furious power is non-interactive. Basically, during combat you ask yourself...
Do I have a Furious Power Charge?
Do I have a heavy-hitting ability off cooldown?
If yes, press the button. If not, don't press the button.
Now, that's something of an over simplification, but what it comes down to is, "Is that a rewarding choice to make?"
I'd argue it isn't because ultimately, while there may be an extra bit of satisfaction in squeezing out that extra 25% damage on an attack, it makes your other abilities feel less satisfying to activate because you're always doing these little mental calculations of "Oh, well I could hit Raging Burst / Smash / etc... right now, but if I wait till I have a Furious Power, then it'll be better."
Basically, it's a trade off between one or two really powerful hits vs. everything else you press feeling lackluster without it.