Hi Shahi, welcome to Cruise-Chat. I haven't had the pleasure of sailing on the Gem, so really can't answer first hand. The NCL ships I have sailed on have been good cruises. Congratulations on your upcoming wedding. No cruise line that I know of enjoys or allows overly inebriated passengers, it's just not safe. As for fun cruises, they are all fun. There will be younger crowds on shorter itineraries. Costa has packages where children sail free, so there are plenty of youngsters on board. Carnival has a fantastic children's program, so there are usually a lot of families on board them as well.
If you have a good travel agent, contact them and they can match the perfect ship for you. If not, find a good itinerary, good price, and book it. You'll have a ball!
Best wishes and once again, welcome aboard!