Even though it is slightly narrower than the A330 seats, subjectively the seat feels more comfortable than the A330 seats. Especially the head rest is really good. In terms of seat pitch you will not feel a difference as compared to the A330 seat. On top of that you have the significantly better IFE, larger PTV, better lighting, better cabin pressure, higher humidity, more overhead bin space, a very slim IFE box under the seats compared to the bulky one on the A330 and in flight connectivity. You will not be disappointed.
If you are a larger person you will notice a difference as compared to the 777 seat, but if you were comfortable on QR's A330 in Y you will be comfortable on their 787.