There are several factors that make Mars of special interest. As a near-neighbor, it moves fairly rapidly, so it is immediately noticeable as more than an unmovable point of light (i.e. a star). But Mars is also of greater interest in this way than the gas giants farther away, which move rather slowly from our point of view. Because of its elongated orbit, Mars goes through a 15-year (or so) cycle of near and far oppositions, which means that it changes in brightness a great deal over time. It is very red, which means it is not simply just another white or nearly-white point of light, which describes the majority of stars and planets when observed with the naked eye. Because it is outside earth's orbit, it isn't tied to the sun as a morning or evening "star" along the lines of Venus (and Mercury to a lesser degree since it is so hard to see under most circumstances).

With the invention of the telescope, it quickly became apparent that Mars was the only planet that one could easily observe where one could see the surface (again Mercury is a limited exception here - it's hard to see, but one can see the surface). Because the surface was visible and it was near the earth orbit, it seemed to be the best extraterrestrial analogy to earth. And the idea that this might imply life has caused a great deal of excitement over the decades.

So there is a pre-telescope fascination with Mars, and one that followed the use of good telescopes. For a good summary of the history of Mars observations, see this site, although there are many others.

This can mostly be attributed to a crazy in the late nineteenth and early twentieth centuries that there might be life on Mars. This was obviously a wild idea, and when scientists said "these patterns on the surface of Mars are too perfect to be natural," people got interested!

A similar phenomenon happened with the moon. As telescopes improved, the moon could be observed with much greater clarity, and people noticed it was covered in craters! Not understanding that these craters were from meteor impacts, they were thought to have been artificially created. It seemed impossible that a bunch of perfectly circular patterns could have happened by chance. Herschel first published this idea in 1790, going so far as to say that the moon was inhabited! He argued that these circles must be lunar cities, and that the lunar inhabitants made them for protection from the sun.

This idea eventually died off, but Mars exploration went through a similar pattern. New telescopes began to notice a series of lines on Mars. These lines looked too perfect, and were reckoned to be a "canal" system. In 1894, Percival Lowell publishes a paper on the topic, claiming he has discovered and mapped 116 canals on Mars. These canals must have been created by an intelligent species, or so it was thought. This craze takes off with the public several years later when an Italian astronomer, Giovanni Schiaparelli, publishes a series of pictures of Mars, complete with blue rivers and green fields. The public goes wild, and the idea of life on Mars becomes a popular sci-fi topic for decades.

Many pictures and maps of what Mars' surface must look like are published. In 1905, a new series of photographs from a new powerful telescope-camera seem to confirm the existence of these canals. It is not until 1909 that a new massive telescope in Europe reaches even greater magnification powers, and shows definitively that these canals are just an optical illusion caused by mountain ranges. The surface of Mars in reality appears barren and inhospitable. Nevertheless, the idea of Martians persists until the 1940s as a popular topic of sci-fi and other works of fiction.

Sources:

-Lane, K. Maria D. 2006. "Mapping the Mars Canal Mania: Cartographic Projection and the Creation of a Popular Icon." Imago Mundi 58, no. 2: 198-211. Historical Abstracts, EBSCOhost.

-Bowler, Peter J., and Iwan Rhys Morus. Making Modern Science: A Historical Study, London: University of Chicago Press, 2005.