Dragonslayer has some weird prerequisites. Iron Will is always nice, but then it gives you immunity to fear effects, so the majority of will saves a dragon throws at you (basically its aura) is neutralized immediately. Two ranks of tumble seems a bit absurd; I'd assume it'd have ranks in the relevant Knowledge for identification.

Energy Resistance, Improved Critical, Overcome Draconic Spell Resistance, and the Damage Bonus all are solid abilities though. If all you're fighting is creatures with the Dragon type, you're set. You'll get the least effectiveness from the Overcome ability assuming the character is primarily martial, but Energy Resistance also is just a bit low for the lack of Reflex saves and Lightning Reflexes doesn't bridge that gap too well.

It does seem like it deserves its score.