To me- the only part outstanding on the bike is the Ultegra. Crankset is a downgrade and the Wheels- even if they are full shimano- is a low quality wheel. But at the price of $1250 would not be bad. I would not rate it as a $1700 bike though. The heart of the bike is always the frame and at this price I would not expect the wheels to be good- and components to be passable. That is what it is. Looked at The Giant site and for the money- you would not be getting much better.
http://www.giant-bicycles.com/en-us/....1/9014/48853/
Lower grade groupset in 105 and the wheels are not top rate but it is a known quality of bike. Dare say Trek- Specialised or any other manufacturer would have bikes around the same spec and price and if given the choice- I would go for the "Known" product. AND- there is always the possibility of last years model or a bit of bartering to get the Price down a bit. So get a test ride on the Diamondback to check it is for you after comparing a similar price bike from other manufacturers.
Sorry to be a bit negative- but as I say- All the diamond back has going for it is that it has some Ultegra bits on it. 105 may be a bit heavier but is not much of a downgrade.