The True Fae are horrifying.
To paraphrase one of the Changeling books: In their realms, the True Faes' desires overrides the laws of nature. They're often hyper-intelligent, but sometimes in ways that humanity wouldn't recognize. They have no real compassion for mortals. They can alter a person's body in anyway that pleases them: distorting their very being into whatever their whims dictate. The fact that they are both alien, yet somehow understandable is scary. They can look like us, talk like us, but from there it's entirely chaotic.
Robust Character Creation:
There are six basic Seemings (character race) and a million more specific Kiths (sub-races) that players can chose to be. In addition, players can combine seemings or kiths until they have a character concept they want to play. This matches the Chaotic nature of Faerie very well, and allows players to create nearly any Fae-being they can imagine. Before this, the main WoD books were very 5x5 (5 clans, 5 covenants for V:tR, same for Werewolf, Mage). Instead the Changeling writers made as many character types as made sense. I've run a few Changeling chronicles now, and a few players have duel-kithed or took duel-seemings, and the level of individuality felt by this was greatly appreciated.
Changelings are able to go into all of these settings: The Mortal World, Arcadia (Faerie), The Hedge, and Dreams. This allows for many different kinds of chronicles to be run: from exploration games (Hedge, Arcadia), Protecting those you love (Dreams, Mortal World), Court Based Politics games (Mortal World, Hedge), epic games of vengeance and rescue (Arcadia, Hedge), and so on.
A straw man has taken over your old life - works your old job, plays with your children, and sleeps with your wife. Fetches can have great and terrible powers, or be weak. They are often antagonists, but can also be made into allies against the True Fae. They offer an interesting and personal being to act against or with you no matter what kind of chronicle you are in.
Contracts & Pledges:
I group these together because they're both the magic of Changelings. I like magic that has a cool story behind it. The fae make pacts with abstract concepts: stone, mirrors, hearth, et cetera. Everything only works for the Fae because they've made these pacts. Nothing makes sense unless a deal has been worked out, and often these are done in the way that allows the Fae to best exploit their contract (catches exists in all contracts to allow the free use of these). Pledges are similar to these. You pledge to another particular being to perform a task or do something, and in return you are rewarded. If you fail, you are punished - by the Wyrd (the mystical, chaotic Fate of the Fae). Player characters can be exploited by pledges and player characters can exploit others by pledges. This offers interest story devices and role play opportunities.
The Seasonal Courts:
It's usually a good sign of a game when I don't know what I want to play. Changeling overwhelms me with too many good options. Many seemings/kiths fascinate me, and all the seasonal courts' goals make sense to me. I like that (ideally) power changes every season, that each season has its own rituals and festivals, and that each Court has unique contracts associated with it.
This technically could have gone with the other settings, but I'm making its own heading. At the Goblin Markets you can trade away your youth, memories, eye color, for any number of odd benefits from the strange and shrewd goblins. Whole stories could also be told about the market - deals going bad, a rare object showing up.
There are other interesting elements to Changeling (entitlements, hedge beasts, goblin contracts), but I feel I've covered enough of the game. I'm a huge fan of Jonathan Strange & Mr Norrell, and I like that Changeling uses the same kind of Fae magic and malicious though gentlemanly fae beings as JS&MN. The game offers any number of thematic ways to play it, but I love the subtitle's suggestion best: A Game of Beautiful Madness.