Coopers is first and foremost for me a bar. They serve food, and good food, but what they excel at is a great and varied beer list. Ive had good salads and frites there so I would recommend it for a date or night out with friends.
The downstairs is long and narrow and when its a weekend it can be difficult to drink there if you cannot sit at the bar. The upstairs is spacious and offers great views of the capital.
Outside seating also makes it a attractive place to go in the warmer months.