The rarest of all celestial visitors visible to the naked eye, comets are capable of, by far, the most variety. When one hears the word 'comet,' the thought of a long-tailed object comes to mind. Yes, while comets can look like this, these 'great comets;' are exceedingly rare. To illustrate, the last great comet, McNaught (above), was visible in 2006-7. Before that, Hale-Bopp (1997) was the last great comet. While there was Hyakutake the year before in 1996, Halley's Comet's 1986 appearance was the last great comet before that. Just by looking at these examples, the pattern becomes obvious: great comets are, on average, a once a decade event.
Now, while not all comets are the pop culture image great comets present, they are fun to look at. With the naked eye, comets can be visible as diffuse fuzzball-like objects in the sky. In binoculars and telescopes, comets can take on a lot more detail, especially in regards to color. For comets, the most common color is a greenish blue, which can be extremely delightful to look at in the telescope as there are no green objects in the sky.
Another interesting point to comets is that they are unpredictable. While forecasters will make predictions about what any given comet will do months in advance of its arrival, comets often have other ideas. A prime example of this was Comet Holmes in 2007, which morphed from a small, normal binocular/telescopic comet just on the edge of naked eye visibility into a massive body as large as the full Moon. The same can be said of Comet McNaught. While bright, no one could have ever expected it to erupt a sky-spanning tail after making its close passage to the Sun. To the contrary, in 2013, the much-hyped Comet ISON promptly disintegrated upon close approach to the Sun. To say the least, comets are true cosmic wild cards that are always worth a look.