New Ideas to mix in:
King veiw: Custom game option. Sets camera extreamly close to land, focused on a king unit (remember the shoguns or whatever from the japanese Civ III scenario? Upgrade system like that, good stats that increase with each era, and command ability (keep reading)). The player cannot move the camera away from the king. So how on civ-earth are you suposed to control other units, or even your cities and diplo? By brining in a new system. As the king, you can give orders: at a special menu, select either unit, city, diplo, civilization, or misc.
Under unit, a list of your units is shown, and when you select one another list shows up. This list contains actions, like move south-west, move east, move to (see below), worker actions, disband, and beyond.
As for Move to, build to, and all things concerning locations, a map is 'given' to you, showing the world, like the normal game, but, this is special. Each tile discovered by exploration is not revealed imediatly. Instead, for discoveries, tiles are revealed according the the king's location; the closer, the faster the tile is revealed on the map, the farther away the tile is, the longer (in turns) it takes to be revealed to you. (ALL CHANGES ARE EFFECTED BY THE REAL GAME ELEMENTS. e.g., horseback riding tech halves the time, and the existence of roads, railroads, airports, or sailing routes effect the time respectivly (if multiple routes exist, the fastest one is used, always).) This is updated every turn, but, of course, a unit discovery of a tile may be several turns old! Talk about realism! As for enemies locations on this map, it is more up to date than exploration, but the effect is aparent.
Under city, a list of your cities is shown. When you click on a city in the list, your veiw goes to the city veiw like the normal game (but without unit positions). You can do all the things you normaly do: change production, adjust worked tiles, ect. but when you exit (and there must be an exit button on screen) you are informed that it will take ## of turns for the changes to take effect. (ALL CHANGES ARE EFFECTED BY THE REAL GAME ELEMENTS. e.g., the horseback riding tech halves the time, and the existence of roads, railroads, airports, or sailing routes effect the time respectivly (if multiple routes exist, the fastest one is used, always).)
Under Diplo, all normal options are available, but once again, responce time is affected by the king unit's location.
Under civilization, all civic, government, domestic, science, spending, and all things concerning your civilization are here. Also under this option, is your map, which is, by the way, the default mode when exiting other modes, next to king veiw. Zoom is available, and clicking on a city, unit, or rival city or unit brings up the respective option.
And under misc, anything I've missed or doesn't belong in any other option is here.
Easy Modding: In the Civ 5 editor, every option or value range, when rolled over, gives a quick description of the option and several examples and what they effect. If no editor is used, then this should be in a how-to-mod quick guide.
Era-specific Interface and Leaderheads: (Civ 4 does not have the latter, so I must write this down here) As the name sugjests, an era-specific Interface: Ancient: Rocklike, ~Classical (?): Paper (Reedlike), Medieval: Paper (hinting of scrolls), Rennaissance: Still paper (hinting of books), Industrial: Paper, Modern: computer screenlike (digital), ~Future (?): Glowing screen.
Era Leaderheads is a definite must.