We just finished our travel on the Mariner of the Seas. It is a beautiful ship with rock climbing, indoor ice skating, miniature golf, inline roller skating, etc..etc. But of all the prior cruises we've been on, we were most disappointed with Mariner of the Seas.
1) The food was mediocre at best. Children's menu were not even better: chicken strips were very dry every night and macaroni and cheese was bland. During our port of Cozumel where many people booked an excursion over 6-8 hours, it was impossible for us to make it back on time for the lobster dinner.
2) The nightly entertainment was just average to below average. The only one we liked were the ice skating show and the Russian juggling act.