You can draw something as simple or as complex as you like, but if your partner doesn't guess the word, then your turn counter gets knocked back to zero. The only drawback is that sometimes, if you play for a long time with the same partner, you'll get the same words over and over, so unless you practice drawing them different ways, it can get a bit predictable.
Here's a few of my favourite drawings that I've done for some friends:
Do you play Draw Something? What's your longest winning streak?