Pros
Working with THAT brand behind you makes the company a pretty special place to be - most of the employees genuinely care about LEGO and its customers which makes for a very positive working environment, though I'd echo what one of the other reviews has said that if you hate the stuff it's probably not the place for you... The company is also very open internally about its projects and plans.
Cons
The company's high growth recently has led to more pressure on every area of the business, which are not always equipped to deal effectively with it. The management structure, especially in the retail arm of the company, has led to a few people far removed from the 'action' holding a lot of decision-making power with largely incompetent middle managers beneath them, so trying to get anything major achieved can be incredibly frustrating. Low employee turnover (while generally a good thing) makes progression within the company almost impossible. Pay & benefits (in the UK at least) is also poor - the love for the company held by most employees is taken advantage of hugely in my opinion.