I love Gal Civ 4, however has some mechanics that make no sense and just kill the game quickly when come upon them. 

One of the major ones is when at war and the opponent captures a colony, immediately converts it to core world if it is over size 2 during the war. 

I strongly believe there should be a restriction not been able to do so until AFTER the peace treaty. What if I do not want to convert every single small-medium planet? There is no way back after I retake them. 

Add also there is no way to create choke points even in GalCiv4. Have to be lucky for a fleet to get stuck in to stop an endless stream of 1 ship fleets attacking dozen of planets per turn and converting all 3+ to core worlds, requiring citizens to be converted to solders in transport ships.