Ramadan is, essentially, a season that commemorates the so-called revelation of the Koran (the Islamic holy book), or more precisely, the beginning of that revelation. The name is taken from the Arabic name for the month in which it occurs. During Ramadan, Muslims observe a daytime fast, eating only before the sun rises in the morning or after it sets in the evening. Muslims are also encouraged to read through the entire Koran, and make sacrificial gifts to the poor, among other practices.
Lent is a 40-day season of the liturgical calendar of Christianity, and is often observed by fasting, self-denial, and almsgiving (giving to the poor). Thus, externally Lent and Ramadan appear similar. However, the similarities end there.
Lent is a time of fasting and self-denial, not in celebration of a revelation, but as a season of contemplation and preparation for the coming Lord at Easter. (Both Lent and Advent are seasons of preparation in this way.) Mirroring the 40 days Jesus spent in fasting and self-denial prior to launching his public ministry (see Luke 4:1-13), Christians likewise fast and reflect on the significance of Christ's work.
In many ways, Lent is not an uplifting or exuberant season, and many Christians seem to resent it because of that. However, life itself is not a constant time of exuberance, and Christ's life and ministry are full of times where his experiences are far from uplifting, in terms of the "mood" of the moment. One of the things that Lent offers is a time to focus on the spiritual dimension of these seasons of life: when things are less than wonderful in every way.
Not to downplay the significance of Ramadan to the Muslim at all-- but it is not very much like Lent in its meaning, purpose, and function in the Christian's life. There is value in using "familiar language" instead of churchy insider-speak like we often use; but calling Lent the "Christian Ramadan" is not really considerate of either.