So I'm pretty well set on making an Episodic Adventure Game set in a Geek culture comedy magic realism setting like 'Spaced', 'Scary Go Round', 'Scott Pilgrim', 'Buffy'.
ON ITEMS: Okay, let's assume that certain main characters should ALWAYS be carrying certain trademark items. To use an example from real life, I don't leave the house without my bag containing my keys, phone, wallet, iPod and a pencil and paper. This could be made interesting if the item in question is iconic. Where would The Doctor be without his Sonic Screwdriver? In any episode of Doctor Who, we assume the doctor has the screwdriver, and we know that it can be used, loosely, to open doors (unless deadlocked) tamper with machines and detect energy and chemicals.
If a character has to pick up an item to use in a situation, should it vanish next episode? Hmm, how about if they borrow it, next episode it'll be back with the character who owns it, and if they buy/take/find it, it's in their house (if large or with an obtuse function) or inventory (if small and possibly useful on a regular basis) subsequently. Within reason, I mean, I wouldn't expect a character to keep an empty crisp packet they used to solve a puzzle!
I'd prefer to keep it down to as few items as possible. No puzzled in which the character is carrying a pistol and must pick up a rock to break a fragile object, when they could have hit it with the pistol or dropped it and had the same effect!
Perhaps there could be a recurring minigame for using some items, like the lock picking in 'Oblivion' or 'Tribly the Art of Theft'. So we ideally want an iconic, multiuse item for the main recurring protagonist. Other characters may later have to solve the same puzzle without this item and so have to find another way around the problem! That'd be fun!
Characters: It wouldn't be too hard to switch between a cast. I don't want to do this too much and end up confusing like 'Heroes' sometimes becomes, but seeing things from another character's point of view and/or using their abilities to solve a problem may be fun. Let's assume for now that we have a main character (with some distinctive items and abilities), a few other major supporting characters, and then minor characters who play bit parts and stuff, much like a typical sitcom or soap opera. It is possible to have a character with two forms, each with different abilities. This IS a little overdone in games, however, so I'm unsure about using it.
Note on characterisation:
Characterisation between episodes CANNOT be effected by player choices, otherwise episodes will contradict themselves. If you were allowed to make character X act like a complete jerk, kill everybody in town and then next episode he was back to his sunny happy self and everybody was alive again, it'd be a bit weird! While I want to allow the player some flexibility on how they solve a problem and what they say, to make it more interactive and add replay value, all the options should be 'in character'. This actually furthers the appeal of playing as different characters in different segments and episodes, because perhaps as the main character you can't punch that annoying NPC because he wouldn't dream of doing it, but playing as a less scrupulous character, you can because that's in character for them!
This makes it somewhat like a JRPG, and yes, I'm going to reference Final Fantasy VIII again, because I think it's an example of excellent characterisation in a game. You play Squall, a surly teenage boy. When given dialogue choices, they're often just the jist like 'accept' or 'refuse' and Squall will translate this into his way of speaking, so 'accept' becomes, '...fine' and 'refuse' his trademark '...whatever'. Sometimes though, weirdly, and I assume this may be the translator's mistake, not the game's, you may get the options in his wording ie '...fine' or '...whatever'. I think the dialogue should be consistent. Keeping answers in the character's voice is probably a better way, because you know how they'll word it. All the choices given should be in-character.