When i saw someone else play jungle Nautilus I could see the shear power of his ganks. If you have caught them out of position they are most likely not getting away. I wanted to try him so I bought him instantaneously, and when i played him I fell in love with him. Hes been my favorite champ since and I don't think any other champion will ever take his place in my heart. :)

These runes help out with the early jungling which he desperately needs because he has one of the lowest base armors in the game, really slooooooooooowwwwwwwwwwwww.......... The attack speed helps him get a couple more attacks in before his shield breaks. The magic resist is to be, well.... more tanky late game.

These masteries help him tank and sustain more in early jungle.

Ultimate>Shield>AOE>Pull

Im only 1300 my self, but nautilus has carried me from 1100 to 1300 so he can help you get out of elo hell.

Uhhhh kidding me! He doesnt have a flaw!
JK he has a bad early jungle and somewhat lacking damage.

His Ultimate is great for Ulting the adc for your team to jump on him.

Nautilus can pretty much go with any team comp. He can turn into a bruiser if he needs to be. He is one of the best peelers(get enemies off of your adc) in the game. Ult there adc, let your bruisers or someone dive him and turn around and peel for your adc.