I probably have
more experience running one-on-one campaigns than I do of multi-player! it probably stems from atarting playing D&D in a small village, where there
was only one other gamer. You either play solo games, or you don't game at all!
I really enjoy the one-on-one format, though it has some significant differences to a normal game
and it can be a lot of work for both player and DM. Most of the difference have already been brought up, but for me, the most noteworthy ones are:
- Intensity: since there is only the DM and the player, interaction between the two is very intense. You are essentially holding a single long conversation. This can be quite draining, and I find that in a solo campaign I need to take short breaks as player and as DM every hour or so, just to relax a little, and to reconsider events.
- Role-Playing: when you don't have to worry about boring other players with immersive conversations, you can get a lot of interactive role-play into the game. Whilst there's clearly no need to do every conversation, there is freedom to spend much more time on PC-NPC interactions. Characters seem to develop a lot of depth in the solo games I have run and played in.
- Demanding: since there are no side conversations between players, there's essentially no break in play except that which you create as DM. As such you really need to know your setting and the NPCs, since they have to be at your fingers immediately. Interestingly, though, I find myself spending more time on the setting, and less on the specific adventure. Since there's no-one else to bow to, the player has a free hand to do whatever he wants, so stories can go off on tangents really quickly!
As for the practicalities of a single character in a D&D game, I have found a couple of things help make the PC's life easier. Firstly, there's no-one else to balance against (except NPCs - but that's the DM's problem), so a character who would be overly strong in a normal game is fine in a solo one. I have a game with a half-fiend PC, and though he has more powers, I don't worry about the Level Adjustment too much.
Secondly, having a few NPCs about to help is fine. In one game, the PC and his sidekick became so close, and the PC knew his personality so well, that in combat I could leave the player to handle the sidekick and just worry about the monsters. That helps immeasurably.
Finally, if healing is a problem, then
bend the rules! Let alchemical healing potions be fairly common. Give out a little more cash to pay for NPC clerics to heal. Make using scrolls easier. I suspect, though I haven't tried, that a VP/WP system might be useful here.
I want to add that, though a solo game is different in feel to a standard D&D game, it is still a
lot of fun... provided the DM and player mesh well in gaming styles!