This arguement isn't only about miedieval first or second total war but many players, complain about change of the brilliant style that has been applied in first medieval total war. Which was that you were moving your armies from region to region, no matter the paths they may take or paths avalible, each move took one single turn. And also that defensive wars were that you defend a region against enemy attackers who move their armies to that particular region. I agree to it that sometimes it feels right. To think of it least, we were rid of that stupid way of flanking, where just because of the game runs in turns, your opponent sends his armies just by your army, to your city. And if the enemy army marchs faster than yours, due to being cavalry, light units or maybe your army carrying siege equipment and such, you can never catch the enemy. No matter how large your own army and how small the enemy army is, he can in fact, rush through your lands and attack a city of his choice. So it looked stupid to form a line of defense in campaign map.
However this wasn't that enormous a problem until Empire Total War where armies no longer need siege equipment, therefore an additional wait turn to attack a settlement. It could be that if you had no one in your non-enemy-bordering settlements, one single enemy unit, flanking through your borders, can capture all those settlements without being touched by your main army. There has been made this area of control fix to prevent this in some degree, but that works only when the enemy is trying to run past you. You are given the chance to intercept which when automated, fails more oftenly than not.
Medieval first total war, was indeed, the first of total war games and for some people, the only proper total war game. Or maybe for some other people, the reason they love total war games. I can not say neither one nor another for myself, as i like every single game that total war has to offer. Was many long years ago when i used to play Medieval I and i spent hours and hours trying to determine how to save my nation. It was really brilliant, and at the same time, epic! You could give titles to any general you like, and this was only avalible in Medieval I. In my opinion, this was a good way to distribute the loyalty and ability to generals of your faction. However, at later total war games, line of nobility was estalished, which was also sensible, but still title system could be included, if not, maybe something similar. Apart from that, in medieval 2, you still couldn't fight wit hthe ships on your own. This was understandable at times of medieval I, maybe even rome total war, but started to annoy most people at Medieval II. How can a game have that brilliant graphics on land and not even any graphics designed for sea battles?
The way that your nation's borders shown on the minimap was at mediaval I, epic, as generally shown in political history maps- However, that has been changed in the second game, to something that the borders of your regions are visible too. So until you had quite large territorial domination, it looked bad, as the borders were too thick to be shown out. The region system had this advantage that you could choose a certain bordering region to be a battlefield.
Since that no one could get to interlands before capturing that place, works especially so in north africa, one could focus his armies on one side, guarding all the rear. As these are the differences between those games, it is up to you to decide which one is better. I think not of that kind of thing and consider both almost equals, and like them both.