To answer the question of this post, they made this game for players like me who have never played a Civ game prior to this. I love Civ 5, being the first one I've ever played. After watching a friend play it, I thought it looked really cool and got it as soon as I was able to. Vanilla was pretty good, albeit the end game felt a bit empty, but the rest was solid. I bought BNW before G&K, so it felt more like I was getting additional civs, but I was fine with that. I really loved BNW, as it touched up culture (I play Japan when not using mods), and the trade routes made the economy feel a bit more dynamic.
I have played Civ 4 (prior to getting G&K/BNW for Civ 5, so I was comparing base version vs base version), and I think it's alright. Unlike 5, I avoided building wonders except the pyramids with a passion as I felt it was ultimately pointless if they were just going to be obsoleted a few techs later. I also felt the unit movement was slow, and there were many turns where nothing happened. In my first game I lost my second city because I didn't know that cities can't protect themselves, and that barbarians could capture cities. xD I never did have a bad experience with unit stacking, but I did find it a bit cumbersome to use. I felt religion was awkward and I hated waiting to get Environmentalism just so my cities could stop being green.
However, just because I have a gripes on Civ 4, it doesn't mean that it has things I actually do love. Seeing predators roaming around in the wild made the game feel more dynamic and alive, as it wasn't just some barbarians against you but also mother nature herself in the early game. In fact, just the concept of barbarians being able to steal my cities was neat. Map and Technology trading was another thing I found pretty cool and also found weird as to why they weren't in Civ 5. "What's that? We both have a tech that the other would like? Well let's trade then!" "Howdy there, Christopher Columbus! I agree, trading our knowledge of the lands does sound like a good idea!" I also liked that each civ got multiple leaders, each with their own unique traits.
In short, I'm glad they made Civ 5 with new players in mind. I may be a youngster when it comes to Civilization, but I'm by no means a strategy casual. I may not play as much as when I first got civ 5, but I can still find myself binge playing whenever I feel like it. I often have a play style of minding to myself and focusing on culture and infrastructure, but as a imperialistic Rome in the middle ages found out in my first game, I finish what was started (One war turned me from a simple 4 city nation into a sprawling world power.
As long as they refine the systems they used in Civ 5, and maybe even bringing back predator animals, city-conquering barbarians, and map/tech trading, I will definitely be looking forward to Civ VI.
Also to be clear, I did try Civ Rev 2, and I feel that it is someone who smashed up a disc of Civ 4, duct taped the shards back together, and called it a new game. (I am not calling Civ 4 a bad game, in fact it would my second choice if Civ 5 stopped working. What I am saying is that Civ Rev 2 is a watered down product of a fine wine called Civ 4).