It has been streamlined and simplified in certain ways, while it has become complicated in other aspects. Unfortunately, all the efforts have resulted in the AI being utterly exposed in it being not so intelligent.
Simplification in terms of research (very streamlined), unit movements (1upt), worker management, meaningless diplomacy, bland and boring victory conditions, wonders being not the game changers they used to be. I might add that city specialization now is less prominent (no decision to run a specialist versus a cottage economy), no sliders. Instant unit buys.
More complicated in the sense that districts and wonders steal real estate, unit movement with religious and military units interfering with each other, UI very bad designed.