The name Pharisee in its Hebrew form means separatists, or the separated ones. They were also known as chasidim, which means loyal to God, or loved of God - extremely ironic in view of the fact that by His time, they made themselves the most bitter, and deadly, opponents of Jesus Christ and His message.
The Pharisees perhaps meant to obey God, but eventually they became so devoted and extremist in very limited parts of The Law (plus all that they themselves added to it), that they became blind to The Messiah when He was in their very midst. They saw His miracles, they heard His Words, but instead of receiving it with joy, they did all that they could to stop Him - eventually to the point of getting Him killed because He truthfully claimed to be the Son of God.
Jesus Christ had strong words about the Pharisees, and what awaits some of them:
"He answered them, "And why do you transgress the Commandment of God for the sake of your tradition? For God commanded, 'Honor your father and your mother,' and, 'He who speaks evil of father or mother, let him surely die.' But you say, 'If any one tells his father or his mother, What you would have gained from me is given to God, he need not honor his father.' So, for the sake of your tradition, you have made void the Word of God." (Matthew 15:3-6 RSV) [see The Ten Commandments and The Ten Commandments Now?].
"How is it that you fail to perceive that I did not speak about bread? Beware of the leaven of the Pharisees and Sadducees." Then they understood that He did not tell them to beware of the leaven of bread, but of the teaching of the Pharisees and Sadducees." (Matthew 16:11-12 RSV)
(Note: Just as yeast causes bread to rise, yeast was sometimes used as a symbol of sinful pride which made people haughty and "puffed up.")
"The scribes and the Pharisees sit on Moses' seat; so practice and observe whatever they tell you, but not what they do; for they preach, but do not practice. They bind heavy burdens, hard to bear, and lay them on men's shoulders; but they themselves will not move them with their finger. They do all their deeds to be seen by men; for they make their phylacteries broad and their fringes long, and they love the place of honor at feasts and the best seats in the synagogues, and salutations in the market places, and being called rabbi by men. But you are not to be called rabbi, for you have one teacher, and you are all brethren. And call no man your father on earth, for you have one Father, who is in heaven." (Matthew 23:2-9 RSV)
(Note: A perhaps somewhat surprising statement - the Pharisees were correct according to their limited perspective, and were to be obeyed by the Jews under their authority. But, they were not to be emulated in their way of life - they were Hypocrites.)
"But woe to you, scribes and Pharisees, hypocrites! because you shut the kingdom of heaven against men; for you neither enter yourselves, nor allow those who would enter to go in." (Matthew 23:13 RSV).
"Woe to you, scribes and Pharisees, hypocrites! for you tithe mint and dill and cummin, and have neglected the weightier matters of the Law, justice and mercy and faith; these you ought to have done, without neglecting the others. You blind guides, straining out a gnat and swallowing a camel!" (Matthew 23:23-24)
The lesson from the Pharisees' example is that self-righteousness is not righteousness, and that God's true people are to live according to all of God's Word, not just certain parts that are most convenient or to one's own liking (see I Did It My Way...).
Fact Finder: What Pharisee was personally converted by Jesus Christ after His resurrection, and went on to become one of the greatest Christians of all time, a man who later wrote a large part of what became the New Testament?
See also On The Road To Damascus