How do I win
Decend until you find the Amulet of Yendor and then return to the surface.
How do I play?
There is a long and detailed embedded help section. But in short, to move, tap. To run, double tap. To walk repeatedly, tap and hold. To rest, tap in the middle (hold down to rest repeatedly). To check your inventory, double tap in the middle. To attack, either walk into a monster, or stroke from the center to the direction the monster is in (this will attack until you're hurt, the monster is killed or runs away). Other options are found in the "Command" picker.
There are just too many commands!
That's actually not a question. NetHack is complex, and designed that way, with extremely rich interactions. A quick google search will turn up various tips, tricks and strategies...
How do I switch between ASCII and graphics?
Rotate the device to landscape or portrait mode.
How do I change the graphic tiles?
While in graphics mode, tapping the "Options" button will show options that include what tile set to use.
How do I go to white on black ASCII? Or turn on the "fake" graphics?
While in ASCII mode, tapping the "Options" button will show options that include various "terminal settings".
I'm having a hard time gettting my gestures to be recognized
You can always just use the command picker, but the display will display your finger stroke as you move - once it recognizes your gesture, it will "snap" into the grid. (It's pretty generous about that - simply being at the right start and end point can be enough for simple things).
How do I cancel a gesture if I forgot how to make (I don't want to make a "bad" one)
Keep scribling until it can no longer recognize the gesture (it no longer "snaps" to the grid). In general, however, most commands can be cancelled (for example, if a direction is needed, tapping the middle will cancel it).
What's up with the fugly icon?
In the ASCII version of Nethack, the player is symbolized by the "@" sign, and you often play with a pet dog (which is a "d"). That character just happens to be ugly in the (only) mono spaced font on the iPhone.
Why the literal port of all the commands, and not some sort of paperdoll style inventory?
Because it's NetHack - you want each and every possible command, because there's bound to be some sort of weird interaction that will be missing if any of the commands are touched.