ESP is only an aid too. It is there to stop any more power going to the wheels therefore you still have to correct your mistake, hence if you do a big slide, you will still slide. However you also have to be careful not to over correct or you will very sorry.
Personally i have tried it out in first gear, going slowly shifting to 2nd and speeding up, then turning sharply and i was very impressed how it dealt with the mistake and helped me correct it. I couldnt even go into a big spin as it cut power due to my foot being floored! lol
Again, ESP will not activate if you are driving properly and smoothly. This is my first RWD car too and i am still scared shitless that i am going to spin it, but for what its worth, its pretty hard to do, but when it goes, it goes