My experiences so far with .915 are mostly good. I even managed to do a number of pretty long continuous sessions (Large Map - Challenging) without the game doing a CTD at all (stability is very good), although it becomes a bit slow at times, specifically in tactical combat (laptop with 8 GB of RAM helps obviously).
Compared to some earlier versions, the aggressiveness of the wandering monsters seems to have decreased somewhat. That's fine, but if you have a creature spawning building in or near your zone of control, you should get into trouble and that should be the same for the AI. It's rare, but there do seem to be some attacks on outposts (haven't seen cities yet) of the AI. But they shouldn't be building outposts, let alone cities, more or less on top of those sites. That's what irks most people in this thread.
But some monsters do actually seek out targets; I've dealt with the wandering Ignis and the Earth Elemental Spawn (I forgot their name except their relatively high stats 13A/18D), which require you to be vigilant when putting settlements near them. That's the game element that should be kept in, although I don't know how to write an AI to handle this properly (as in putting some guarding units near such a place that spews out annoying wandering units from time to time). On the other hand, if the monsters become too aggressive, you use that tactic to loot their sites, which was done in earlier versions.
The champions thing is somewhat annoying, but they have very limited hit points after having been killed previously, and by that time I usually roll over my enemies anyway. What I would like to suggest to compensate, is that you get to pick off some of their possessions, that would reward you for taking them out better. That would even save them in some cases, since I saw Magnar cast Berserk on himself, even while having already equipped a Berserk item, with which he killed himself, because of his low remaining number of Hit Points.
The thing that makes the game work for me, is that you have to think of new ways to get the most out of your situation each time. That is, items you pick up, the location you start off with, the abilities you get, the heroes you get and so on. These variations keep you on your toes and make adapting very important. The only problem I guess, is that the AI simply cannot keep up with a smart human player.