Wow, 6 answers and already 2 snipes by ppl who don't even play 4th and thus can have no idea what they are talking about.
Dragonbreath in older edition was quite binary. Either the players found a way to negate it, at which point the dragon was better off not using his most iconic ability. Then the dragon is reduced to claw/claw/bite like an overgrown lizard.
Or it was too powerful, killing the mage and rogue outright on a failed save. That does make for exciting stories, but makes certain game elements, such as an ambush by a dragon, rather difficult to do. Furthermore it makes the initiative check in a combat extremely important.
The 4th Dragon Breath is nasty. It will hit all or many of the PC, costing most of them ~1/4 of their hit points and giving them a crippling side effect. that is enough to be scary without being binary.