For one (of many), in Civ IV by the late game, because production was fast you would have every building built in every city. There was not much strategy to that. In V, building is slower and you can't build everything everywhere. You need to think long and hard about what you want a city to accomplish and build buildings accordingly.
No, there's not more strategy here. There's a reason why I could waltz through this game on Immortal on my third game when Civ 4 is still a struggle for me on Emperor. And I'm not even an avid Civ player. Although you can build fewer buildings, they made it painfully obvious which buildings you should build. There's fewer buildings available and most only give one kind of benefit and generally the only penalty is maintenance. You may be able to build faster in Civ 4, but there's lots more buildings available so you're building nearly all the time. Many buildings have multiple benefits and penalties and until the end game, it takes a lot of skill to figure out which one to choose. Even two science specialised cities in Civ 4 could have taken very different build paths as was needed, but in Civ 5 the build queue for each kind of specialisation is so obvious you may as well save the queue for each. And there's fewer specialisations required because of the game's much simpler mechanics.
Furthermore, the wider city radius and the lack of growing cottages means you no longer need to specialise tile improvements. The city will not use anywhere near its capacity, so you mine the hills and spam TPs everywhere else and simply switch priority to production or gold as the need arises. Every city thus has high production capability, so all you really need to decide is, "If this city is a science specialist and there's science buildings available, build one. Else, if there's economic buildings available, build one. Else, if their's happiness buildings available, build one. Else, build a workshop" and so on. It's not hard at all.
With Civ 5 having taken away so many mechanics and reducing the number of variables considerably, a lot more players are able to see a clear strategy to victory. I think this is where the argument by many who like it better come from, that Civ 5 feels more strategic. I know it sounds patronising, but I think many of them played Civ 4 like a simulation instead of a strategy game, because there were too many variables and the game felt too organic. There was a lot more strategy in Civ 4, but you have to spend a lot of effort on it to figure it out.
Civ 5 is a lot easier to "solve". The variables have been reduced to a handful of numbers which are your "dashboard". Very much boardgame like. They tell you how things are going - if one number gets too low, it's obvious what to do about it. Everything is much more loosely coupled than before, so you can adjust one aspect of your empire without affecting others. The only shared variable is money, so just spam TPs. If all the numbers are good, then just keep pressing End Turn. Once you've figured out the few simple rules to optimise the game, it really just plays itself.