I like some of the ideas for improved features in Civ 5 suggested in the Civ Fanatics' Forum, such as:

(1) Developing more than one technology simultaneously.

(2) Working on more than one construction project simultaneously.

(3) Technology diffusion possibility between adjacent civilizations.

(4) More intricate spy capabilities, such as spreading propaganda against an enemy to persuade other civilizations to combat or reduce trade.

(5) Return of colonies, requiring far less maintenance than cities, yet useful for acquiring rare resources or providing a base for espionage on distant civilizations.

(6) Movement bonuses along rivers (at least when going downstream).

(7) More advanced military units (germ warfare, star wars, neutron bomb, suitcase nukes carried by spies).

(8) More leaders & civilizations:

(a) Iroquois, Led by Hiawatha. Organized, adventurous.

(b) Navajo, Led by Manuelito. Artistic, religious.

(c) Arabia, Led by Abu Bakr. Scientific, adventurous.

(d) Persia, Led by Darius. Religious, adventurous.

(e) Celtia, Led by Arthur. Aggressive, artistic.

(f) Huns, led by Attila. Aggressive, adventurous.

(g) Russia, Led by Ivan the Terrible. Organized, scientific.

(h) Bantustan (Bantu peoples; apologies for lumping them together)
Led by Cethswayo. Aggressive, organized.

(i) Songhay, Led by Sunni Ali. Commercial, religious.

Never heard of Tojo, but Sid Meier, whose probly semitic, might frown ata pop Hitler.