First of all, the idea for this game is based off of Maplestory! If you've never seen it, look at screenshots of it:
http://www.mapleglobal.com
The game would start at a create a character screen. Here you would have a choice of 4 species: Lenny, Skeith, Aisha, and Lupe (Or maybe a whole new neopet created just for this!)! You can also pick what color you are: Red, Green, Blue, or Yellow!
The game starts out at DoN headquarters. It's tutorial time. Judge Hogg talks to you about how he's so glad you joined the force! Then he tells you to complete a training course. During this course, you learn to use weapons, Inventory, and you get to beat up a few wood baddies for training...like a wooden darigan, MSPP, etc. During this training you gain some Exp. and you level up at least once.
Once training is over, Hogg tells you that petpets have run amuk in Neopian Central and that you need to find out why. This is your way to level up. After cruising the maps of Neopia Central, you find the source, which is an Evil Meepit! You now have to defeat the meepit. once you do, all the petpets calm down. Now you go back to Hogg and collect your reward, which would be Defender Armor, a small weapon, and official membership into the DoN!
Now he tells you to find some quests of your own until big news happens. Now you can go out into the neopian world! Now you enter into a different part of Neopian Central with shops where you can buy armor, weapons, or potions. Also there is a portal out of the city, to the great beyond.
Once out of the city, there will be wild monsters: slorgs, muant neopets, theves, etc. Also there will be a way to get to each neopian land. These will serve as the places to get quests and stock up. You would have to take a boat to the islands, and there WOULD be a cooking pot, as you could create new weapons. Also, you can buy petpets to help you. After you get to a certain level, you might get an alert from the DoN to help get a big bad guy like Kass, or Clown Chia, or Eliv Thade. These bosses would give you better stuff as you beat more and more!
If you'd like to give your ides, i'm going to write up a big paper on the idea!