) i'll start with the following.The game is Rifts. For those of you who don't run it and don't know much about it, it CAN be the kitchen sink of gaming. Literally anything is possible, and since this is true, I think it's perfect to illustrate where we cut the PC's greed off and start enforcing your rules (not THE rules, YOUR rules...as by the book, many silly things are possible if you're a stickler for grammar and known for liberal interpretation).
Rifts can be pretty exciting, but also very stressful for a GM because of the possibilities. You can have HU conversions, which, to me, throw everything completely out of whack. In Rifts, I tend to draw the line at super powers because they don't have any resource management. Most powers just happen and there's really not much of a way to combat how they work (there are a million ways to be invisible in Palladium, some of the best are in HU, for example). PF conversions aren't as problematic, though the conversion itself can create interesting problems (how does magic armor go from having AR to no AR when all its doing is becoming harder and not covering more of the body? Mind you, I can give a reason, but it's my own assumptions).
N&SS has it's own problems converting over. People have created entire websites dedicated to transitioning N&SS abilities over to Rifts so they make more sense and don't contradict...then Rifts Japan happened and threw everything upside down again creating parallel powers with the same names and intent that do two different things.
Enough of that, let's get to the point.
The group is set in Kingsdale. It's independent, it's the hotbed of Crazy, Cyborg and Juicer conversion, it has a Headhunter academy, a powerful Mage Guild, a nearby ley line (nexus not toooooo much further off) and a ruler with an invincible mansion. Wilks, Northern Gun, Wellington and NE all have giant warehouses there as well, it's difficult NOT to find something you want as long as you have the money or can trade the right favor.
There are a lot of angles to take a game here from. It can be heroic (The CS comes knocking on Kingsdale's door finally, fight to defend from Uncle Skullhead!), it can be gritty (a group of hoods working out of Dredgetown steal a relic from the mage guild to sell to the highest bidder) or it can be really dark (same hoods, same relic, only the highest bidder is a demon lord who wants the hoods to do his bidding with it).
Pick something, show me your creativity. THEN show me what restrictions you'd put on the players at character creation. Do they have to pick geographically regional classes (mostly North American), are races restricted the same way? Or do you let them bring things from the outside?
If you do...do you allow conversions? As I mentioned above, they can be silly. In Rifts, since anything can happen, you can do the contrived and whacky thing of just bringing challenges that fit the player's power level, or you can use the environment. If you do that, suddenly the GM is the one restricted. He'll have juicer wannabe thugs at his disposal, as the PC's hang out in Dredgetown, but the PCs themselves are demigods with superpowers and Phase World tech.
I suppose that's the real core of it. If you limit the PC's, limit yourself? If you don't limit the PC's, open the megaverse wide and cackle from behind your screen? One thing I've noticed about some GMs and players is they effectively fight a cold war with each other as they game, upping the ante constantly. PCs do something crazy, GM lets it slide but reminds them if they keep doing the NPCs can too...I've always been of the mind that NPCs do what they are supposed to. If they're skilled they exploit their strengths. If not, they flail about and die pretty fast.
To avoid this, we tend to set boundaries at the beginning. Though as I mentioned above, do you restrict AFTER character creation. In Kingsdale, as the example above, you can get just about anything you need. So do the PC's buy LRMs for their black market purchased MK VII APC and rain death down upon various parts of the world, invisible until the last minute because of TW enhancements? Do you "punish" them for obliterating the countryside or do you look at the environment of the game and go, "huh...there's really no one out that way who could do much about that..."
These are just thoughts I have from time to time about GMing. I hope they were slightly entertaining. If you're willing to tell me how you sell your players on restrictions, or how you guide them into making the choice you want them to for the game you're running, feel free. Anecdotes are fine, I love stories and examples.
Depending on players and their gaming history - I know some special power gamers, which I would restricted with available powers, equipment and so on.
