Simplicity
Explorer
I've tried to kludge together one-on-one D&D sessions (fairly unsatisfactorily) for a long time. The Gestalt rules go a long way toward helping with filling out party roles when there's only one character, but I think it would be very nice to finally have a well-designed system capable of running one player parties in normal published adventures.
Especially for those of us married fogeys who find less and less time to get the band back together...
All you really need is some way of beefing up the character that maintains their power at slightly above the power of a 4 player group (slightly above because single players are a heck of a lot more vulnerable than a group... one failed save means disaster in 3.5e). Not that that's all that easy to do.
To survive in a one person party as is, you almost need to add a fate token system or something just to deal with flukes of the dice that normally can be managed just fine by a 4-person party.
Especially for those of us married fogeys who find less and less time to get the band back together...

All you really need is some way of beefing up the character that maintains their power at slightly above the power of a 4 player group (slightly above because single players are a heck of a lot more vulnerable than a group... one failed save means disaster in 3.5e). Not that that's all that easy to do.
To survive in a one person party as is, you almost need to add a fate token system or something just to deal with flukes of the dice that normally can be managed just fine by a 4-person party.