Many dictionaries define "Christian" as someone who professes belief in Jesus as Christ or who follows the religion based on his life and teachings.
(Also see: The Bible’s Viewpoint - What Does It Mean to Be a Christian?; WBTS)
Jehovah's Witnesses do believe in Jesus and follow his teachings. They believe that Jesus is extremely important...in fact he is the second most important person in the universe next to God Himself. Jehovah's Witnesses teach that no salvation occurs without Christ, that accepting Christ's sacrifice is a requirement for true worship, that every prayer must acknowledge Christ, that Christ is the King of God's Kingdom, that Christ is the head of the Christian congregation, that Christ is immortal and above every creature, even that Christ was the 'master worker' in creating the universe.
So yes, by every genuine definition, Jehovah's Witnesses are Christians. Even disinterested theologians and secular dictionaries acknowledge that Jehovah's Witnesses are a Christian religion. In fact, Jehovah's Witnesses are a true restoration of first-century Christianity.
The reason that some falsely accuse Jehovah's Witnesses of not being Christians is because they use an artificial, trinity-specific definition of the term "Christian" which excludes anyone who does not believe that Jesus is God Himself, rather than the Son of God.
Jehovah's Witnesses do not believe that Jesus is God Himself. Rather, they believe just as the Bible describes Jesus - as the "Son *OF* God".
Nowhere in the Bible is it mentioned that Jesus ever claimed to be God. Rather, he specifically called the "Father...the only true God." (John 17:1-3; Also see John 20:17; 2 Corinthians 1:3 and 1 Corinthians 8:6)
Nowhere in the Bible does it say that Jesus is God. Instead, the Bible repeatedly refers to Jesus as the "son of God". Because the Bible says that Jesus' "origin is from of old, from ancient days" (Micah 5:2), the Bible shows Jesus was created by God. Jesus is:
the "only-begotten Son" of God. (John 1:14; 3:16, 18; 1 John 4:9)
"the first-born of all creation". (Colossians 1:15)
"the beginning of God's creation". (Revelation 3:14)
The Bible shows that Jesus is subordinate to God: "The head of the Christ is God." (1 Corinthians 11:3) Jesus himself said: "The Father is greater than I." (John 14:28)
For much more, see: