Hawke is a Black Hole CO with slightly stronger than average units and strong, but relatively expensive CO Powers.
Hawke is not an inherently difficult CO to use, and is a very solid choice on many maps, but there's a few points worth mentioning. His 110/100 d2d bonus gives him an edge on non-tower maps against 100/100 COs, especially in 2 Hit KO situations where you want to eliminate enemy units quickly and efficiently. With a tower, his 120/100 infantry, tanks, and artillery are all quite powerful on offense. Unlike Lash, for example, he is not reliant on specific terrain to recieve his bonuses, so no matter what situation your units are in, on attack they always benefit.
His COP and SCOP are not flashy, but they certainly get the job done. 9 health units are much less effective than 10 on both offense and defense, and 8 health direct units like tanks will have a lot of trouble keeping up with your recently healed 10 health ones. Hawke's powers are great on long and large scale attrition games, where he can continue to harrass the health of his opponent's entire army while repeatedly healing his own.
Both powers, however, take a significant time to charge, and many other COs will be able to fire off their own COP or SCOP before you can. You'll have to plan around surviving your opponent's powers first in most cases. On the bright side, in many cases this disadvantage can actually help you, as you benefit the most from the healing aspect of Hawke's COP and SCOP this way. Try to keep most of your units alive during this period, because if you lose a unit entirely, you definitely won't be able to heal it in this manner.