You will have a GREAT cruise. The detractors are people who compare ships, but if its your first cruise you won't be thinking about that, so just enjoy the experience. Epic is a cool ship in many ways...
DO book your show reservations online well before the cruise (right away), so you can get the best showtimes. All the best ones are free.
DO see the Slam Allen band and Howl at the Moon. If you pick a dining room use the one with a stage (the aft one) - they have the Legends at Sea shows in there which are great.
The Brazilian restaurant (sorry, name escapes me) is the best. If you are going to pay extra do it there. Le Bistro was so-so on Epic.
I didn't care for the Cirque Dreams & Dinner show, but if you try it, sit as close to the action as possible.
You MUST see Blue Man group. Go twice if you can, it is always different.
Oh - find all the lightswitches in your cabin during the day. By nighttime it is too late, you'll never see them.