I can't comment on excursions as I don't know what ports you're visiting. But I was on Summit for almost 3 weeks last March/April (we did a week around the Caribbean and then stayed on board for the repositioning across the Atlantic - it was awesome!) and we adored it. The staff are tremendous, especially Gary Walker, the British cruise director who made our cruise so special for us.
We have sailed 20 days on the Summit (2 cruises), amd we loved every minute.
Carnival Liberty New Year's Eve 2007
Liberty of the Seas 5/2008+11/2009
Allure 1/16/ 2011
Independence of the Seas 12/29/2013 Top-notch!
Among other problems on the Summit, I had a terrible washroom in my cabin. Mold and mildew all over the floor and shower tiles, a shredded and dirty shower curtain, black all around the mirror, dirty toilet, and very few toiletries. My showerhead did not work, as is the complaint on so many of these posts. No amount of asking for the cabin to be cleaned seemed to bring any response. I didn't even see or meet my cabin stewardess for the first three days.