Posted December 23, 2018
Vingry: One thing that I'd like to say about the game however, which I think only applies to a minority portion of players from the whole Civilization series fanbase, is that I always find the midgame to be boring. Probably it's due to the fact that I often find myself aimlessly researching stuffs with no real endgame objective in mind. Again, this opinion of mine would probably change the more I play and get accustomed to the game.
I could wrote paragraphs and parahraphs about Civ 4! Here you've got some thing I can think that make midgame interesting. In the mid game there are some "universal" milestones, such as the race to Liberalism (first one to research it gets another tech for free, anything that is already researchable) or the development of Scientific Method (you initially lose science input because monasteries become obsolete, but it opens the path to other powerful technologies that you will need in the next turns).
Also by midgame, if you are playing in a map with different continents, you get access to Caravels and Astronomy, so you get to meet (and invade) a whole set of new civilizations. A bit later comes the Rifle, which is possibly the biggest leap in terms of military technology, and the perfect point to get an advantage over your enemies (more or less at the same time as drafting units become possible with Nationalism -drafting Riflemen is the most cost effective "rushing" action in thr game).
Also during Renaissance / Industrial Age several National Wonders become available, which are crucial to specialize your cities.
If you keep playing you will discover more subtleties and challenges as you go on.