I visited there for work four times last year. At first I was not impressed, as the office was out in Kanata where there’s nothing to do. But in later visits, I stayed downtown and had a great time.
Since it’s the capitol of Canada, it does have a lot of things to see.
Winterlude is cool, but when I scheduled a business trip to coincide, the weather was too warm to skate on Rideau Canal or keep any ice sculptures solid.
The downtown area is great for pedestrians. Last time I stayed at Novotel and just walked everywhere.
The National Mint was interesting…you can tour the factory with gold and silver everywhere, and lift a gold bar (chained down of course ;-).
The National Gallery was great. I went twice. You can see my comments: http://www.43places.com/entries/view/1055941