I'll give it a try then...
1. It's a true team format. Quite apart from the semi-team format offered at Prereleases, Emperor games requires cooperation among an actual team that can work together during an acutal game. This adds entirely new dynamics to the game, in which you have a vested, lasting interest in members of the game that are not yourself. In free-for-all games, you at times might aid another player, but only as it is expedient at the time to serve your own efforts. In emperor, the lieutenants have actual interest in defending their Emperor first and secondly each other, if they have the means to do so. I think that's exciting. One thing I really like about this is that instants, especially combat instants, grow in utility, as the number of combats you are likely to use them during expand to two for each player.
2. The rules of the game change. The rules set that I favor the most currently is that all players can target two steps away, attack with creatures one step away, and that global effects remain global. Decks must be built differently, with these considerations in mind. The Emperor, in particular, can't even hit their goal target when the game begins.
3. We haven't tried it yet. This argument is more of a synergy of the other two, so I may be cheating. However, the Emperor format offers a whole new range of considerations both inside and outside of the game that would make for a much different experience than the one that we're used to, and to varying degrees, have all gotten tired of. From team formation to deckbuilding to the actual gameplay, it would be something new. Much like the 10-card format we tried for a while, it should be enjoyable and bring the whole game a new perspective.
