This is a great alternative to busy Dublin! It is a lot less busy, but there is still a ton to do and a great night life! People are very welcoming, and there is a very rich history of the town. It is easy to navigate and easy to get to (a 10 euro bus from Dublin via Aircoach).
Insider Tip:Become friends with the locals, i.e. people working at your hostel, because they know the best spots to go for a great Belfast nightlife experience!