It would be awesome if you could run into and ally yourself with more types of arcane creatures other than those available through the diplomacy techs. Rather than just one possibility at each level it could be random between a couple of different types depending on what you discover in your explorations.

So, more magic creatures that can be found natively without being summoned. More minor creatures earlier and the possibility of just a single unit willing to be bribed into joining your civilization much like champions right at the beginning of the game or after learning a diplomacy or adventure or magic tech of some sort.

Also, it would be great if the full stats of summoned creatures showed up on the learning spells screen plus in your spell book. I don't know the game well enough and haven't memorized each possible creature so it would be nice to be able to easily see its full stats and abilities so you can weigh the pros and the cons of different summoned creatures depending on what you might need at that moment.

It would also be nice to be able to level and enhance your arcane creatures be it those who join your army or those you summon.

On a sidenote the dragon needs to get its move increased. It can fly so one would think that it shouldn't get movement penalties or be only as fast as a man on foot (its speed is only 2). At a minimum a move of 4 and more appropriately a five or six as it should have no problem outrunning a horse logically.