k, here goes
in 2.25 the cd acutator was introduced. Also, the action actuator alloed animations to be played simultanouesly [if they used different bones]. Also, the NLA editor was introduced. Many of these features required a “publisher key” which could be purchased from [now gone] NaN. You can download a free key now, but since the game engine is back this doesn’t gain you anything.
since publisher no version of blender has had certain features which still now cause people problems. With a publisher key you could sign, lock, compress [once signed or locked] .blend files. These files cannot be opened by ANY other blender version. The publisher key also unlocked the features I mentioned above [nla, actuators, … stuff], but also unlocked an option to export a standalone runtime.
the next version of blender since 2.25 didn’t have the game engine [parts were not open sourced, notably the collision detection library: solid]. Blender did not get the game engine back until version 2.32, which introduced new bound types for dynamic objects, but little more.
Since 2.32 the python implementation for the game engine has changed significantly, and the logic and physics are no longer run merely every frame [though, using python they can now be configured to work that way]
logic runs at a fixed rate [independent of framerate and physics] and so does physics [independent of framerate and logic]. This has been source of some problems, but it really is something people should get used to.
Also, with the new timestep the physics is a lot more consistent at different framerates, but still everything behaves differently. Different values in motion actuators and the like are required than those in 2.25
from my experiments with older versions of blender [I started using blender version 2.21, but have tried versions as old 1.8] this has happened a few times [the forces required changing], most notably with the introdcution of 2.20 I guess.
2.36 also introduced some rendering speedups [objects off the screen are no longer rendered], with associated bugs [armature deformed objects mess up sometimes]. Also objects are now drawn in sorted order for alpha faces, and if that isnt’ good enough, the ztransp button in the material buttons will sort by faces in multiple objects [at the cost of speed]
this is all a rambling from memory though, no accuracy is guarnteed.