Oligopoly is a market structure that can foster either competition or cooperation behavior and generally is correlated to higher profit rates. Economists would rate this market structure based on performance as

1. Poor because firms will invariably collude to raise price.
2. Mixed in that firms can take advantage of economies of scale and thus lower production costs and have better records for technological innovation, but earn economic profits which leads to higher prices and lower output levels for consumers.
3. Excellent because firms' high profits benefit shareholders who are also consumers, so all of society benefits.
4.  Economists do not make such judgments on performance because it is a value judgment.