Yes, most definitely, it is Christian. It is one of the original Christian faiths, and many of the other Christian beliefs share Catholic ritual. The core belief in Catholicism is that Jesus Christ came to the Earth to abolish our sins, and to show the people that God had a human side. Another religion that is close to Catholicism is Episcopalian.
Though Catholicism has some beliefs that are not shared by other sects of Christianity. The core belief is that Jesus Christ came down from heaven as God's son, lived a sinless life and then died for the sins of man. Catholics believe all of this, and therefore are Christians. They just have some additions to this that other Christian sects do not believe.
Catholicism is a sect of Christianity and is considered to be among the Christian religion, just at individuals who are Baptist, Methodist, and Protestant are considered to be Christians. Catholicism has specific rituals and practices that are unique to the Catholics, just as Baptists have specific rituals and practices that are unique to the Baptist sect of Christianity.
Simply defined, "Christian" just means the religion believes Jesus Christ to be central to their belief system. Technically, Catholics DO place Jesus Christ centrally within their belief system. However, Catholics, like all the other branches of Christianity, have their own unique take on it. They believe in the intercession of saints to request attention from their god and the deified Jesus Christ, as well as his mother and what they call the Holy Spirit. Most Christians believe in a direct relationship with their deity.
First of all, I would like to state that I am not a Christian, but even still I can argue against the Catholic Church being Christian. Christianity takes on many different forms and many different sects and branches. However, there are some forms of Christianity that remain more true to the bible than others. The Catholic Church has changed 10 of God's commandments, thereby rendering it up for skepticism of truly calling itself Christian. The 4th Commandment by God is "Remember the Sabbath Day, to keep it holy." However, it is the 3rd Commandment in Catholicism and they celebrate the Sabbath day on Sunday. Nowhere in the bible does it mention that the Sabbath day is on Sunday, the bible adamantly repeats that the Sabbath day is the 7th day of the week. The 7th day of the week is Saturday, not Sunday. Sunday is mentioned in the bible three times, but with no relevance to the Sabbath Day. The reason the Catholic Church has the 4th commandment in the slot of the 3rd commandment is because the Catholic church omitted the 2nd commandment from the bible which states: "You shall not make for yourself an idol in the form of anything in Heaven above or on the Earth beneath or in the waters below..." The Catholic Church condones the worship of idols of the crucifix, of the angels and saints, and the blessed Virgin Mary. The Catholic Church goes against the bible's principles, in this regard. They celebrate the Sabbath on the wrong day, and they worship false idols that represent Heavenly things, and call themselves a Christian church because they worship Christ, but other Christian sects would argue that to truly call yourself a Christian you worship Christ and uphold the bible's commandments and principles.