Is staying in Belfast for a week too long?

Yes. There are things to do but it seems a lot of time when there are things which can be done.

Is a piece of string too long?
You need to be more specific when asking questions.
Are you travelling alone or in company?
Is it during summer or winter?
What kind of budget will you have?
What kind of activities do you like - history, culutre, shopping, eating, partying?
Is this part of a longer trip or are you travelling for one week only?
Do you get up at half 11 and stroll around the streets or wake up at 6am with a laminated itinerary?

I promise it’s not as you thought,
because there are many cityscapes and histories for you to study and experience.
The culture of the city is old enough to explore, I think it’s worth taking time to travel.
The city also be famous of shipbuilding in the early 20th century, you can experience as more as you can.
If you take more attention on the things that are unique in the city,
you must find something extra interesting than you thought before.
Hope you enjoy your trip. :D
Edited by: ingridtseng

I promise its not as you thought.
I bet you didn't know there was lots of shipbuilding history to explore.
It depends on why you are going there and what your interests are but a week in one place without any daytrips probably is too long.

It just depends on what you want to do..... I prefer to take my time, then it might be even too short ;-) But sure if you just want to visit the highlights quickly, you will be done in 3 days :-)