I have played around enough with v2.5 in Both BGEE/SoD and BG2EE to make some comments.
Summary: I feel pathfinding has degraded significantly. It has gone from being annoying to potentially being game breaking.
1) When you spawn into some areas you can have several party members merged together. Most of the time I can get them to break apart, but in the mod Southern Edge, the PC never appears again if you go to the Southern Edge from a location outside of Athkatla (this is the game breaking one if you don't notice in time and over write your saves). I am not sure if mods are particularly at risk, but this is what I have seen up to now.
2) Parties now freeze (get stuck) if you try to move them where they overlap their current position (reposition in a small area). This one comes into play most when you spawn into a battle. I used to be able to select positions and for the most part everyone moved with minimal interference. Now, the party freezes for 6-10 seconds and then one at a time moves out. This is deadly for a combat spawn. I am now forced to micromanage moves in combat WAY more then with the old pathfinding and even then since I need to wait for people to get clear, it takes more time to reposition the party.
1) I don't have party members permanently stuck behind immovable things anymore. Eventually they move out and around.
Did not notice any other benefits. They could be there, but I didn't see any.
I wanted to call these out especially since the first downside can break a game if you are not careful with saves.