Besides Starcraft, what other games have you tried editing/modding/using its custom features???
Here is a list of few experiences of mine:
Halo 3 has this small map editing tool where you can place things anywhere on certain maps. I made this house that had tons of mines and jump pads and when someone goes in and kills a mine, their bodies gets launched through the chimney.
Warcraft III has one of the best editing tool. You can change anything you want from stats of all heroes to scenic looking terrain. People have created really good modded games like Dota. I am still playing through the campaign. I have also played the default custom maps. When I played the sheep map for the first time, I was easily amused by how my unit was moving using keys. I forgot that map making on war3 wasn't as limited as SC.
I don't have the skills to enjoy DotA. Just one mistake or asking a question and people get really mad. At least I can enjoy playing lots of rpg maps people make or any hero arenas.
Little big planet is a 3d graphic side scrolling game like super mario bros. Players can also create their own levels. I've tried to make a level similar to super mario but failed. Fortunately, lots of other people have done it too and i've seen couple youtube videos on it.
Kingdom hearts is an disney/final fantasy - adventure game. It allows players to customize and build their own space ship in a lego like way. I've made one thats shape like an FF airship (sort of).
My boyfriend likes his Half-life, Guitar hero and soul calibur. Half-life has this program called Gary's mod. It allows people to mod the half-life game completly. I've seen it, Its really complex, Its like the Sims for guys.
I heard Guitar hero now has a music editor where you can share and create custom songs. This is only on Guitar hero 4; we only have Guitar hero 1-3.
Mario paint was a game I enjoyed playing back in the day. It was a super nintendo game that was basically MS paint equipped with a mouse controller and pad. One of the cool things i've customized was the music sheet. I even recreated the theme from tetris using Gameboy and Star notes.
None.