I agree Civ 1 -> Civ 2 -> Civ 3 -> Civ 4 progression seemed to be enhancing on the same good bones framework. Although some may question some of the new concepts introduced in each minor/major upgrade, it did not break that it was essentially a great game concept. Civ 5 broke that progression. It does not feel like an enhanced Civ 4, like Civ 4 felt like an enhanced Civ 3 and so on. As for the mass market; really after Colonisation II, the dumbing down had started. It had good graphics but poor game-play. So the coders who made Civ 5, had previously worked on Civ:Rev and Colonisation, so the outcome of Civ 5 was in hindsight expected.