Pros
The people I worked with were fun and talented. Tons of restaurants around Ubisoft Montreal. Great job security. Beer on Fridays.
Cons
Tech sharing and management is a disaster. As a programmer, prepare to spend a lot of time integrating and merging features from other projects. The management is completely full of itself and convinced that Ubisoft makes the best games in the industry. There is very little looking into what other companies are doing. Very little innovation, most games apply the same 'game loop' of open up an area, do the quests in that area, go to new area, rinse and repeat. You will be expected to do a LOT of overtime with almost zero compensation. If you work 400 hours of overtime, you're lucky if you get 40 hours in vacation. Someone who leaves Ubisoft for a year and then comes back will almost always have a better position/salary then if they had stayed at Ubisoft.