When we where there 14th July to 4th August, Margaritaville where not taking reservations, although if you go to the Kiosk just down from Bubba Gumps, i think they will make reservations for you.
We found we did not really need them at City walk or in the parks with the exception of Mythos.
We ate at NBA where not sure about eating here ,but we had a lovely meal in it and will eat there again next year. Finnegans, at Universal was another place that we had a good meal. Pastamore at Citywalk was excellent, as was Bubba Gumps, Margaritaville was very good as was Nascar. we also ate at Bahama Breeze on IDrive highly recommend it.
You also have the restaurants at the onsite hotels, only ate at RPR , in Jakes and Islands Dining room and both where very good