I'm too late to help, but make a note of the Keltic Kitchen for your next trip. It is on 28 in West Yarmouth on the southbound side of the road. There is usually a pretty good line, but it is worth the wait if you want a nice hearty breakfast. They cook up a great Irish Breakfast and also have other brunch offerings as well.
I never found a great breakfast spot in all the years living on the Cape..nothing like the Black Dog on the Vineyard. Some like Gourmet Brunch. They do fresh OJ. We used to go to Perry's on Main St. His oatmeal was decent enough. My requirements are real maple syrup and homemade baked goods. Breakfast burritos too. This is hard to find on the Cape.
There is a new pizza place on Main St. that many love.
The Indian restaurant has a good Sunday buffet and cheap. Misaki has great sushi. Golden Fountain has great Chinese. I too am not a fan of the Roadhouse but my friends love it. The same friend had a lovely dinner last week at the Island Merchant on Main St.
My teen and I love lunch at Common Ground. It is run by a religious earthy bunch but they are not preachers and just serve a decent healthy meal for a great price. What makes the place unique are the homemade booths..you have to see it. I was there two years ago and bought some lovely homemade soaps.
I always count on the Roadhouse in Hyannis for consistently good food. I have to mention that I had a great dinner at the Island Merchant on Main Street this past week - more casual and a funkier atmosphere than the Roadhouse and less expensive. Great food, bbq and Caribbean inspired - and the service was also very good. They offer half portions as well. I have also had a wonderful and more creative meal at Hannah on the corner of Main and Sea Street. Haven't been there for over a year so not sure how it is these days but if you are looking for a more cosmopolitan feel to your dining experience this is the place. Not Your Average Joe's, at the Cape Cod Mall, is a small Massachusetts-based chain with an interesting menu and fabulous foccacia bread with garlic-parmesan olive oil dipping sauce provided at each table. For breakfast, many people have recommended Collucci Bros. on South Street in the past. A lot of folks recommend the Gourmet Brunch on Main Street but my limited experience there has been just so-so.
Gourmet Brunch? Are you kidding me? Roadhouse has the reputation but I've never been impressed. Especially the time I went there on a special occasion with the wife and couldn't get any lemon for her salmon. Had to go to the bar myself and ask for some lemon...quality D. Columbo as you sat there at the bar with that $#@! eating grin on your face. My wife won't eat salmon now because the piece she had was at least two days old and you guys were basically cleaning out for your "annual" short term closing. Weak, don't waste your time or money at the Roadhouse.
Totally agree with Not Your Average Joes response. That foccacia is kickin. However, on a down note, sorry, the sirloin tips I had were no good and I regret not complaining but my mom was taking me out for dinner and gave me half of her meal which was actually pretty good. Good luck on Cape Cod...usually hit or BIG miss!