Total War does have its random elements. Combat is decided randomly, for example. The thing is, when you have thousands of individual soldiers on each side of the fight, and each soldier has its own values for elements such as attack strength, defense strength, health, and experience... the random element tends to average out, making combat much more predictable.
The most random element in the game are the soldiers themselves. They don't always do what you tell them to do, because among their stats are courage and impulsiveness. Nine times out of ten they might, but that tenth time is what makes you grind your teeth.
Will they rush headlong into battle, disrupting a carefully crafted strategy because the prince and his bodyguard are trying to make a name for themselves? Will they break early, turning what should be a meatgrinder for the enemy into a route for your side because the new conscripts couldn't stand up to a single cavalry charge?
Watching an elite unit of cavalry get surrounded by pikemen and cut apart because they were having too much fun cutting down retreating peasants to heed your recall orders is frustrating, especially when its led by the heir to your throne.
And then there's the time it takes to resolve a single battle. There are so many elements in a battle, that large ones can last forever. I once spent fifteen minutes in Total War just deciding what units I wanted to bring in first, the order reinforcements would come arrive, considering the lay of the land I was defending, and positioning units for maximum effect. The battle itself lasted an hour. There were two huge armies involved, so there were breaks between engagements as my attacker and I waited for reinforcements to arrive and to redress our battle lines before resuming the fighting.
On the other hand, it was exciting to watch the battle unfold. The whistling hiss of arrows, the creaking and thuds of catapults, the ring of swords, the rumble of charging horses, and especially the screams of the wounded and dying all make for an exciting battle. But that single battle, and tidying up afterwards, was all I did that day.
I personally like CIV's abstract combat system. Even the largest battles can be resolved in less than ten minutes. It's just that with so few units involved on each side, you feel the effects of luck, good or bad, much more strongly than a more tactical combat system like Total War, where even the smallest battles take time to resolve.
