The album simply lack the variety, it is enough now not to let faster songs and ballads play alternately in succession. Also sound technically sound "A Girl Like Me" as the first album - a lot has therefore not done - still is compared with the 1st album to recognize more autonomy Rihanna. It has all potential and a lot of light the 3rd album is indeed better.
Conclusion: With a bit more time, creativity and the last finishing touches would have made "A Girl Like Me" can be more. Therefore, "only" (but still) 3 stars.