Strengths of Utilitarianism
Utilitarianism takes into account consequences, looking just at intentions with no regard to consequences seems impersonal. For example, keeping someone alive who is suffering in pain ignores the consequences as a deontological approach would.
Utilitarianism had aims of happiness and avoidance of pain that are desirable and it makes sense as we do seem to be motivated by pleasure and pain.
Utilitarianism considers others and not just the individual. It it concerned with the common good and considers all who are affected.
It seems straighforward to apply and concurs with common sense about trying to achieve the desirable goal of happiness.
Weaknesses of Utilitarianism
Utilitarianism is concerned with the greater number, happiness of the minorties may not be protected.
Utilitarianism seems to ignore intentions and individual motives; actions have no moral relevance.
Utilitarianism requires the outcomes of an action to be known when they can't always be predicted.
To decide which act will produce the greatest happiness, alternative actions and their possible outcomes have to be considered - this seems impossible.