An excellent article by Elaine Sternberg exists on "The Social Affairs Unit" blog: Why Ayn Rand Matters: Metaphysics, Morals and Liberty. Highly Recommended.
Ayn Rand, in a very real way, is the 20th century's anti-philosopher. She was quite the contrarian, and is hated amongst the 'elite' philosophical establishment to this day.
What did she say that pissed so many people off? Well, here is a simple listing of premises she held:
1. Reality is objectively real. (i.e. relativism is false)
2. Liberty must exist for man to reach his fullest potential.
3. Capitalism is the only truly humane economic system.
4. Attempts to mitigate other's sufferings by economic redistribution ultimately makes everyone worst off, even those on the recieving end.
In a nutshell, Rand was ripping the foundation out from underneath modern liberalism. Having lived in Soviet Russia during the revolution and its aftermath, she saw first hand the evil that is unleashed when liberal thought is taken to its logical conclusion, and realised that the premises of liberalism were demonstrably false.
No wonder she has so many enemies...