Half-dragons have a +3 level adjustment. Let's look at what you get for that (all this is assuming you're playing some kind of warrior class, otherwise, why take a half-dragon?):
+8 Strength - Unquestionably, very nice, probably the best thing about the template. But since you're down 3 BAB, you only get a net +1 to hit, and it knocks your attack progression back significantly.
+2 Con - This in no way makes up for losing 3 hit dice worth of HP
+2 Int and Cha - Not really very useful for a warrior
Immunity to an element - This is nice, as elemental immunities are hard to come by. Usefulness depends on the element in question and how often you encounter it.
Breath weapon - Good at low levels, but the damage quickly becomes insignificant. Also, the save DC will probably always remain quite low.
Natural attacks - These seem fairly weak
+4 natural armor - Good up until you can acquire amulets of natural armor, then much less useful.
Flight - Only Large or larger half-dragons get wings, which means PCs won't have them.
Does anyone think this is worth 3 character levels (meaning you'll be behind on an attack 60% of the time)? I'm just not seeing it.
+8 Strength - Unquestionably, very nice, probably the best thing about the template. But since you're down 3 BAB, you only get a net +1 to hit, and it knocks your attack progression back significantly.
+2 Con - This in no way makes up for losing 3 hit dice worth of HP
+2 Int and Cha - Not really very useful for a warrior
Immunity to an element - This is nice, as elemental immunities are hard to come by. Usefulness depends on the element in question and how often you encounter it.
Breath weapon - Good at low levels, but the damage quickly becomes insignificant. Also, the save DC will probably always remain quite low.
Natural attacks - These seem fairly weak
+4 natural armor - Good up until you can acquire amulets of natural armor, then much less useful.
Flight - Only Large or larger half-dragons get wings, which means PCs won't have them.
Does anyone think this is worth 3 character levels (meaning you'll be behind on an attack 60% of the time)? I'm just not seeing it.