This is a very complicated question, and one that is very much open for interpretation, but I'll take a stab at it and hopefully fill in some holes.

When Gorbachev came to power, the USSR was in a dire decline. The economy was stagnant, the leadership corrupt, and public support at a low. There was a very credible fear that the experiment of communism would result in a failure. Gorbachev, a scholar of both the West and traditional Bolshevism came to the helm at the apex of this crisis. Gorbachev's answers to Russia's problems were two policies: perestroika ("restructuring") and glasnost ("openness"). To put them in basic terms, their aim was to reinvigorate the economy by slightly relaxing the reigns of government control in a way that would be viewed much like successful New Economic Plan that improved the economy greatly after the Russian Revolution (and its detrimental war-time communism).

The problem with this image of a newly-invigorated yet still traditionally Bolshevik Russia was that perestroika and glasnost called for more collaboration with the West, and more capitalist policies (which, naturally, the aforementioned corrupt leadership didn't like). For example, he opened the door to a lot of western companies, such as fast food chains, and tried to root out corruption.

The public's view of Gorbachev's policies was split over perestroika and glasnost.. which is very accurately and briefly portrayed in this Russian Pizza Hut commercial: https://www.youtube.com/watch?v=fgm14D1jHUw

So what were Gorbachev's aims? In short, to maintain a communist tradition in Russia by modifying it for the times. He wanted to ensure that communism remained a viable option for Russia (and others!) in the 21st century. Perestroika was NOT a last ditch attempt to save the USSR. In fact, many economists argue that it was a well formulated policy, but it was too little too late.