Also named the "Play CTP as it should be" Mod. Lots of lots of small but significant changes.
i. addressing gameplay imbalances; and
ii. extending the scope and depth of gameplay.
Changes from v3
i) a modified Trade system designed to encourage Trade;
ii) a revamp of Governments in order to allow for more interesting choices between them;
iii) the improvement of Science buildings to make the Science v Gold decision more valid;
iv) the primacy of Air Power to make the Modern Age more interesting; and
v) Great Library updates for all the changes and entries for all the new units and advances.
Without doubt a file you must try.