So listing the issues:
1. The integrated bracelet. This is a big turn-off for me, especially since Seiko aren't offering a rubber alternative.
2. The price, considering the movement inside. This one surprises me, because IMO the movement is just part of the watch, and I've seen watches (Panerai) that cost thousands while featuring workhorse movements. Sure, the TO is Seiko's most expensive 6R15 diver, but it's still in the same ballpark as the other offerings. I have zero problem with this choice as the 6R15 has served me well and offered reasonable accuracy in the 3 Sumos I've owned.
3. The existence of the Sumo at half the price and the MM300 that can be found used at close to the same price. That's a huge problem because those two have huge followings.
4. The design, but this is subjective and many people didn't like the Sumo when it was released, but it became a hit.