Manbearcat
Legend
The disease track is something I really want to experiment with in greater depth in my own hack. For various reasons I'm in a bit of a bind as to how to proceed with it due to certain design decisions which militate against numeric penalties as a standard part of the thing. I'll figure out something interesting though. I'd really like to see it become a whole other aspect of the game that the characters have to think about and deal with.
Another poster that I like to read that doesn't post enough anymore!
The great thing about 4e is that there are so many levers to pull and buttons to push. And its quite intuitive what the impact will be because the system is so mathematically transparent. If you just use healing surges and - 2 to various defenses or skills as punishment for the Disease Track, you're going to have exciting, scary results that don't bog the game down.
The greatest opportunities that 4e had (mechanically) to be even more awesomerererer was the default game being more Healing Surge intensive, a robust Healing Surge economy (perhaps whereby players can cash in a surge for a bonus but risk a system specified complication), and the xp system really pushing play toward risky, swashbuckley heroics (eg rewarding failure and stunting) and tightly coupled to players' themes, paragon paths, and epic destinies. The Quest system did a great job with the latter part, but it could have gone further.
There was also a large opportunity area to synch the mechanics (PC-build side and general resolution mechanics) of noncombat conflict resolution and combat resolution.
If I could have a D&D 4.5, those would be at the top of my wishlist.