I have an awesome problem going into next semester: there are more games that I want to run than I could possibly actually run. So I'm going to toss them up here and see if I can get some feedback.
The first I've been considering is Fields of Blood. For those unfamiliar, FoB is a sourcebook devoted to letting players rule and run realms under D&D3.5. As far as setting goes, I'm considering a Norse / Germanic / Northern European land of Black Forests and grim peaks, where the cunning nibelungen dwarves of Niflheim can craft whatever you desire for a dread price, and the Fey Folk of the woods are dying out as the power of the realms of men waxes. To the north is the Grey Sea, and to the south lie the Howling Hills of the wulfen beastmen. The realms of men are fractious, tenuously united beneath a High King, but with each of the noble houses scheming for its own advantage. Notable source of inspiration of the Song of Ice and Fire, as a lowish-magic northern European highish-lethality setting. The PCs enter this milieu as landless humans, disinherited second or third sons of minor lords, minor knights, upjumped peasants, highwaymen on the run, that kind of person, probably around 8th level, and proceed to carve out lands and titles for themselves.
The advantage of the FoB approach is that it solidly grounds the PCs in the gameworld. Their actions have consequences, and there are incentives for involving themselves in local affairs. They take squires, lead crusades, hold castles, marry ladies fair or strapping young knights, and have children who grow to be the next generation of PCs. On the other side of the same coin, though, is the necessity of a well-detailed setting for the PCs to go conquer, as well as the addition of an extra 'realm layer' of mechanics for me to keep track of and prep. I also expect that balance issues may be magnified in FoB as compared to 3.5; a 9th-level wizard can decimate an army with fireballs and teleport out if things are going badly, while a 9th-level fighter simply can't, to say nothing of realm-level capabilities like scrying and other powerful divinations. Timescales are also a problem; time in FoB is measured mainly in weeks. Casters gain here, as well, from the increased availability of time for things like spell research and item crafting; fighty-types have no similar 'downtime'-burning mechanics. Finally, it isn't very flexible as far as player availability goes; if the General of the Armies can't make it to one session, you're kinda hosed.
The other approach I'm considering inverts these advantages and disadvantages. I found a used copy of the Necromancer Games version of the Wilderlands of High Fantasy Campaign Setting, and want to run an episodic game set there, played in the open-table style. Basically, play would be divided into short, one-session adventures, corresponding to a single episode of a TV show or a single short story in an anthology. I intend to draw on the Thieves' World anthologies and Fritz Lieber's Lankhmar anthologies for inspiration (though I should probably also read up on Conan as well). A typical session runs as follows: I prep a hook and a session's worth of opposition. Players show up, with veteran players assisting new players in rolling up characters at an established 'baseline' level (probably in the 4th to 6th range) while I do a little more prep. The Heroes assemble in a seedy tavern in the City State of the Invincible Overlord, get their hook, and go do their thing (along the lines of the Beyond the Black Gate post linked above with the word episodic). The session ends with them back where they started, but richer and more experienced. XP is awarded by the numbers, so players who show up more often tend to level faster. I'm considering using one of the old-school "Spending GP on ale and wenches gets you XP" rules so that leveling doesn't end up being terribly slow (13 encounters per level is a few too many for me...).
The open-table part comes in with the easy entrance and exit of PCs; if you have a new player (or if somebody dies), they get a new character. If somebody decides not to show up one day, no big deal; larger shares of loot for everyone else (if they survive). If somebody decides never to come back, it's bad, but the campaign goes on. This allows new players to 'dip their toes in', so to speak, without committing to spending n hours a week on the game. This style of play also saves me prep time; prep consists of rolling up a random objective, assembling some opposition from one or more monster manuals, and embellishing as I go. This style of play has another advantage, in that it parallelizes well; if I need a week's break and I know another decent DM (and I dare say that I do), I might be able to hand a week's session off without giving away any big secrets or burdening them with a huge amount of work. Heck, I could even alternate weeks of DMing (or, better yet, roll each week for who's DMing), and play in the campaign on my off-weeks. There are two obvious disadvantages here, though: the first is the inverse of FoB's boon, namely that the PCs are terribly disconnected from the world. They're itinerant sellswords doing dirty work for gold, not holding castles and leaving grand marks on the world. The second disadvantage is of down-time; with no standardized (and probably not even any specified) amount of time between episodes, item creation and spell research suddenly become hugely ambiguous. I'm considering turning item creation feats into 'per-episode' resources; for example, Brew Potion might, at the beginning of each episode that you show up for, let you roll up 2d4 random potions that you brewed since last episode. You get 'em at no cost, but they spoil at the end of the episode. Scrolls could work similarly, but wands would be much trickier; perhaps a variant of Crafting Points as a per-episode resource would work.
The third and final option that I've been tossing around for a year and a half now is to run a derivative of Ben Robbins' Western Marches campaign. This, however, would be a ton of work for me, and I like the Wilderlands as a setting well enough to run that instead. Then there's the other crazy option, which is to run Fields of Blood in the Wilderlands, but then I lose the flavor that I want in FoB and have to put up with the craziness of the Wilderlands.