Following great advice on here and watching Youtube I've been able to master Monarch difficulty and could probably have a go at Emperor, but I've come to notice the inadequacies of the AI just like other players who have studied the game carefully. Often's the time when I have invaded an AI without building a full army (in an attempt to get an advantage from a new unit before the AI can counter it for example), and ended up being worn down and in a stalemate situation (particularly when besieging the capital), and my initial army is dwindling to nothingness while the AI's city still has enough health to sustain itself. Now I would probably, eventually, be able to take the capital by keeping up the pressure on the AI but it would become a long and protracted process building new units and sending them in, so I decide it's best to make peace. I'd take peace on fairly even terms to be honest or with a tribute of gold but to my great surprise the AI offers up one of its other cities, often quite a big and useful one, for peace. To be honest it seems too eager to do this, when it could be consolidating its forces and fight to the last. Oh and the other thing that is really bad is when you invade and AI and it sends half its army to invade one of your city state allies, leaving its homelands (even its capital) badly defended. I hope Civ6 will do something about this. I guess the only cure for these problems is to move to Emperor and hope that the Ai's massive cheating will compensate for its inadequacies.