There is no way to generalize shortcomings and advantages of GMOs. It all depends on their characteristics, their traits, the genetic background, the uses (and possible abuses) and many different other aspects. It is also dependent on the will to use them responsibly and in a socially equitable and sustainable manner.
As with any technology: you can use them safely, wisely and fairly. And you can use them differently.
One big con (excuse the pun) is that producers can become beholden to seed suppliers and that we loose a lot of biodiversity. If local growers keep their own seed the crops become specific to the region and there will be other sources of seed if there is a problem, but if all seed has to come from a particular company if may not suit local conditions and if a problem develops what alternatives are there?