Most commonly, the Artificer is pointed at for several Caster Level tricks that abuse spells with no built in Caster Level limitations(Use Magic Device checks to push your Use Magic Device result high enough; simulate a massive CL; cast spell which doesn't have limits). This requires a VERY liberal reading of the RAW, however, and the designers have confirmed that the RAW was not intended to allow the trick, as Artificer Infusions aren't supposed to be placeable in normal magic items.
Other than that, I'm not sure what would be considered broken about the Artificer.