We have had numerous breakfasts at Captain Cook's because we stay at the Poly.
If you get there early, before the major rush, you'll be fine. If you get there at 8:30 or 9:00, it'll be crowded.
Food is standard CS fare except for the Tonga Toast which is the same though cheaper than Kona's version. You can also get Mickey waffles, a breakfast platter (eggs, bacon, potatoes and such), and typical Disney CS breakfast food like muffins, cereal, and the like.