How do you say "it has been a while" or "it has been a long time"?
Example:
It has been a while since I've gone to the cinema.
OR
I haven't gone to the cinema in a while.

Question

How do you say "it has been a while" or "it has been a long time"?
Example: 
It has been a while since I've gone to the cinema.
OR
I haven't gone to the cinema in a while.

Answer

"Faz tempo que...”

In the example you gave, you could say:

Faz tempo que não vou ao cinema.

good luck!

Answer

Picking up your examples: 
1) "It has been a while since I've gone to the cinema", you may say: Faz tempo desde a última vez que fui ao cinema or Há bastante tempo que não vou ao cinema.
2) "I haven't gone to the cinema in a while", you may say: Eu não vou ao cinema há bastante/muito tempo.

Hope this helped :)

Answer

I agree with Ana, you can say:

"Faz tempo que..."  or  "Faz muito tempo que..."