We know more about Mars than any other planet, with the exception of our own homeworld of Earth. We've stared at it through telescopes, sent orbiters and landers, and are even planning manned missions. We are doing everything we can to learn as much as possible about Mars.
What intrigues us so about this little Red Planet? The possibility that humans could live there.
Once we learned how torridly hot Venus was, and how cruel she could be to our vehicles, we kind of lost interest in her and put all our focus to Mars. Don't mistake me, Mars is also contrary when it comes to Earth's metal go-seek-ems. The Mars Curse eats about half of what we send there. Still, we persist because, by gum, we're humans!
Ever since we first peered at Mars through telescopes and saw what might be seasonable variability, we can't help but turn our attention to it. At first we thought the changes might be evidence of a growing season, then we saw canali (channels), which got mis-transliterated to "canals". Imagine our disappointment when the Mariner 9 missions sent us back images of a dry, desolate, pockmarked world. Broke our hearts. We were so hoping it was host to life.
But we haven't given up yet. As we map Mars, we've discovered a vast system of river channels and possible lakes once upon a time, and we've detected water ice in the polar caps. While the low atmospheric pressure of Mars precludes any liquid water on the surface, we believe water may have flowed there at one time, maybe even oceans (aka the Wet Mars theory). The Viking landers had an astrobiological component, and every lander since has been searching for water, a necessary chemical for life as we know it. It is still possible that extremophile life could be extant on Mars, we just have to know how to find it.
As for human occupation? Living on Mars still captures the human imagination (Mark Watney, anyone?). I know Elon Musk has a plan, there's the Mars One project and NASA's consideriing a manned Mars mission, though you might have to wait for the next hiring window to open if you're interested in going. (Also astronauts don't make as much money as you'd hope they would.)
Until then, we'll observe it from afar and send more robots.
There's so much we could talk about on Mars, from its volcanoes to its (lack of) magentosphere, to its iron oxide redness to its thin atmosphere to its damp past and more. I favour a Wet Mars theory, though I won't dismiss a White Mars theory.
Hardcore about Mars, because why would you want it any other way:
What do you love most about Mars?
Do you think we can find extant life?
Should humans create a long-term colony on Mars?
Her Grace is happy to talk about Mars anytime. She's written several post-grad papers about it.