I definitely like realism, historical accuracy and so on. Reading the civilopedia and finding out about the real world through Civ has always been an awesome thing. Going from the dawn of civilization to the future era is a major point of the fun. Assuming we are talking about historical accuracy & realism, I voted 'not very important'. As in, it is not the be/end all. I like Hearts of Iron 3 for its historical accuracy and hardcore realism but it comes with a hefty price - it is a pain in the ass to learn properly and to get friends to start playing it. Civ games tend to be relaxing and enjoyable. C5 is in some ways less realistic than 4 and more in other ways. The techs, buildings and units are still things that only vaguely connect to their real world counterparts so I see little difference there. Regarding the 'science based on population' concept. Less realistic than Civ4 but not that all that different. There's more to science than just population in C5. Specialists, Great scientists, national wonders, science buildings, bulbing, turning gold into technology through research agreements, specializing cities, social policies. I think it is an improvement. C5 is a bit more like "R.U.S.E."; an excellent new RTS that is very streamlined and not difficult to understand and play. But (and this is not easy to pull off) it has great depth too.