Ghasts aren't overpowered. But, they are annoying. Very very annoying. Especially coupled with the current spawn rates. If keep your wits about you there's really no chance that a ghast (or even 3 or more) is going to kill you without hitting a pigman and starting a riot. Of course you really aren't going to be able to kill them back unless you fight in the right terrain in which case they extremely easy to take down. Like I'm not wearing armor and I'm using only a melee weapon easy.
That being said I'd like to them changed in a way that actually makes them dangerous, directly, but also gives you more opportunities/options for fighting back.
Coming out alive (but still flaming), and then it just goes plop.
Yeah, I'm pretty sure I've seen Ghasts die from both fire and lava, though I'm not completely sure.
I kind of think that Notch saying in twitter about making them immune to fire was actually just a joke, and he didn't really mean it-unless a more direct statement was made somewhere else. :tongue.gif: