Just wanted to post these impressions after playing 4.2 for several hours.
First of all, I've been in a lan game (with one other person) for about 5 hours wit no OoS problems, so well done there. We're both running in windows xp service pack 3 compatibility and based on what some people have been reporting I have a hunch that this prevents some CTDs.
In any case, my suggestion:
The AI (especially colored dynasties) is not building new workshops, they are not buying ones for sale, and they don't seem to be upgrading their existing workshops. This is the case even as the game progresses and they gain more than enough finances. To me this is a huge deal, since not only does it make them less competitive, but it also makes the marketplace pretty empty of important items.
Related to this, there are a huge amount of buildings for sale at the start of the game (and they aren't being bought up by the AI as noted above). Again, this is problematic because it means there aren't many worthwhile items on the market. It's also just not as much fun seeing all of these empty/idle workshops.
The legacy mudpack took an interesting approach to this problem. It made it so that shadow dynasties would automatically occupy ownerless workshops but they would remain for sale so the player (or ideally also a colored dynasty) could still purchase them.
So, my suggestion is to consider implementing that "fix" and also tweaking the AI dynasties so that they actually build, buy, expand, etc. They do seem to be upgrading their houses, but that's it.
Thanks for reading and considering my thoughts/suggestions.