the first reason i like civ 4 more than civ 5, is that the tech tree seem more natural to me. every tech either develops a new military unit, a new civic, or a new building/wonder, and sometimes more than one. in civ 5 there are several techs that just improve production or happiness or some other minor effect. the second reason is probably the biggest for me, the cpu actually offers a significant challenge, even on normal difficulty, at least for me. the third is that wonders have a significant role in the game. oracling bureaucracy can net you some hefty bonus points, and pyramids give you early access to representation for your gp farms for example. the primary reason to get wonders in civ 5 is for the culture bonus, most of them are useless enough that it would be faster to get the bonus the wonder provides by building the corresponding building/unit.