The atmosphere is cordial, relaxed. And you'll have all kinds of things to talk about. Around the pool. Or along the promenade rail. And don't be surprised if you find yourself making arrangements to meet them aboard the ship again next year.
Passengers can vary from ship to ship and cruise to cruise.
Cruising is ideal for people traveling alone, because it's so easy to meet other people. In fact, most ships have parties just for singles - early on, so you can start to be involved right away. Most ships also have single cabins as well as single rates for double staterooms. In many cases, a cruise line will even find you a roommate to share a double if you ask them. Pack like you would for any resort.