I'm going to be running a Harry Potter game in the near future, and I don't really know what system would be best for the kind of game that I want to run. The vast majority of my experience is in D&D of various stripes, with a dash of GURPS and some homebrew systems for flavour.
Unfortunately, there really isn't a D&D system (that I know of) that ports well into a Harry Potter game. The spell system in Harry Potter has a lot of stuff in it that doesn't really work well with D&D's spell system, and if a system requires that I rewrite giant pieces of it in order to make my game work, I'd rather find a new system.
Here are the salient features of the game:
- The Harry Potter setting. This means that the system should be able to handle magical creatures, various forms of spellcasting, as well as modern technology in the same system.
The Harry Potter spell system. Spells shouldn't be a strictly limited resource, it should be hard or impossible to resist a spell once it hits you (for the most part), and learning new spells should be easy, but not necessarily trivial. I don't necessarily need to have the spell list from Harry Potter already made for me, but creating individual spells as a GM should be easy to do, so I can make up a few dozen for my players to choose from at the start without spending tons of time on it.
I'm not really leaning towards any specific kind of spellmaking system. If it's a GURPS-style system, where you build a spell based on its effects and all spells need to be built beforehand, that works for me. If it's based on magic words that mimic the faux-latin of the books that can be combined on the fly, that works too. As long as the system is robust enough to let me make most or all of the spells from the books eventually, and each spell doesn't take a ton of time to make.
- No huge magic/martial gap. I'm used to D&D, where your optimal option was to be a full caster, and anything else was going to end up worse barring some serious munchkining. I'd like a system that doesn't say "magic will solve all of your problems", and that makes non-magical action just as good in its own way.
- A dark tone. The players will be wizards (or sentient magical creatures) that never went to Hogwarts, and are both politically and economically disadvantaged. Characters should be able to die and have bad things happen to them, and the system shouldn't assume any zaniness. In addition, this criteria makes most direct Harry Potter systems non-viable; all the ones I'm aware of have significant investment in the house system and Hogwarts, where this is a campaign about adults who never went there.
- An ideal system should contain robust systems for stealth, espionage in general, combat, social interactions, and a basic system to handle player wealth.
In general, I'd prefer a system that's more narrative that simulationist, though that's not a hard criteria. I'm looking for a system that will help me tell a story in the Harry Potter world, and not one that will help me simulate the world and have the cards fall where they may.