Personally, I feel he stopped being so by "Unthinkable", if not earlier. Frankly "Unthinkable" seemed like a symptom of the character's exhaustion rather than his actual shark jump moment. Is he still the coolest, and if so, why? Try to keep the evidence from within the last, say, fifteen years.
Despite Doom's general abuse for the past few years, it's my opinion that he is still Marvel's most well-developed and coolest villain. Nobody else has managed to maintain the level of complexity and characterization Doom has without a turn toward being the hero, like Zemo did.