Pros: casual, friendly atmosphere.
Cons: poor quality product, lack of concern for employees.
Olsson seems to be a fairly typical civil engineering firm. While not a terrible company, I wouldn't say they stand out in any way either. The company is quite inefficient, and doesn't seem willing to make investments to improve productivity. Management seems rather inept when it comes to using foresight, or making important decisions when they are needed. The focus here really appears to center on extorting clients and exploiting employees. This is reflected by an extremely high turnover margin.
Olsson is too big of a company to write a fitting review that may really be applied to everything. Their team structure means that your experience here will really depend heavily on the quality of the team leader you work under. As management doesn't seem to push out poor quality team leaders, its your roll of the dice.