Just read through everything. I think. May have only skimmed some stuff. I meant to take better notes so I could make comments on things that came up months and months ago, but forgot.
Caeli, it may interest you to know that I've seen quite a few people use the term "Mary Sue" in regards to male characters, and with two specific instances in mind, male writers. I don't personally use the term because I find it too catch-all, though, and agree that "Wish Fulfillment" is better.
If it's not too late to give my GMPC suggestions, I'd like to offer the following:
My compromise involving this method is to play a character who is much more interactive than your average NPC, but who will play little part in the actual plot. When I was running a monster hunter game, I played a semi-crazy girl who constantly stayed in the safehouse, occasionally providing tidbits of prophetic wisdom. In my "Hellboy/Cyberpunk" game with the BESM setting that I'm currently running, I'm playing a girl whose mind is trapped in a computer and who can send out various drones for reconnaissance and computer hacking.
The major problem with GMPCs arises, I think, from the "Chosen One" scenario. Group RPGs should not have a chosen one, because if you're not playing the chosen one, you're not the star. Chosen groups are fine, but the players need to be the star of the game in all aspects. And of course, if it's a solo GM game (one person GMing while the other just plays a single character) that single character can be the Chosen One.
This is probably significantly truer (or is it "more true?" What's the right English usage?) in system games than in RP. Some people will find some appeal to this, but you're really better off trying to let each character shine in some individual way.
If you remember that every one of the PCs needs to be important, and your own character needs to be less important than the PCs. This leaves plenty of room for actually playing, because you have any number of NPCs which can keep things going.
Now, granted that sandbox games put the lie to this, but I've had games become sandbox when they weren't meant to be. People are still posting in the monster hunter game even after I already wrote up the epilogue, just because they wanted to keep going with their characters even though I let the game shut down because they were the only two left.
If you're running a pure sandbox, you may or may not want to have an NPC who administrates everything. Certainly a High Queen Empress is going to shine more than the other characters, maybe players are alright with that, maybe not. In that case, you just have to make sure that the characters are free to meet up and chat with each other even if you aren't around.
example that always stuck with me was when they were playing Buffy the Vampire Slayer, and the GM played Buffy. The rest just kinda stood around, watching, as Buffy did her thing. One of them commented, "This is like being the torchbearer." Another said, "Torchbearer? I'm the one holding the flashlight! I am the torchbearer!"
I'm really not good at avoiding rambling today, I guess (sorry!), but it shows the overarching theme of keeping NPCs on all the menial tasks and letting PCs be awesome, whenever possible. It's very easy to see how in a game with rank, where someone is the Captain, that can be pretty much impossible to do.
I think I'd suggest with such games that, if you're going to have a Captain, you don't want to see the Captain too much off the bridge. Although I have little understanding of real-life rank, in TNG
, Picard actually seems to do a lot to isolate himself from most of the crew. In the few times when he can be seen in the local drinking hole, everyone actually pauses and thinks it rather odd. I have no idea if this is actually part of RL or Starfleet regulations or not, though I'd be curious to know.
I think that if I ran a game with a Captain, I'd want someone that I trust, as well as someone with whom I can give either PMs (online) or hand signals (tabletop) in order to subtly steer the direction of the game. Few things in my games would be quite as valuable as being able to have the PC Captain decide, "You know, guys, on second thought, let's NOT steer the ship into that black hole. I don't think it's really an illusion after all." Having that kind of quasi-GM would be fascinating to see work in action.