These are the things that I think are the most important:
Simulation
- Explosive links (dynamite)
- Allow timers to be put on armadillos in level edit mode, so they disappear after a certain time
- Allow portals to be attached to nodes and movable
- Option for unlimited length links in level edit mode
- Allow building links outside level boundary in level edit mode
- Toggling nodes between being anchored and non-anchored
- Functionality for smaller adjustments to node position and tension and timer values
- Keep selection active after start/stop simulation, to facilitate easier editing
- Make it easily apparent if material/tension/timer prices have changed from the default values
- Expand/collapse level sets and solutions
- Make armadillo view for each armadillo
- Make tracking view for each armadillo as well as all armadillos
- Review criteria for displaying 'level failed' message