It's quite hard to know exactly where to start with the changelog as put simply, so much has changed.

Engine

Constructed and implemented a whole new engine to LCPDFR including timer managers, backup managers, suspect managers, AI managers, process managers and event managers as well as event handling and error handling
The ability to start multiple instances of scripts e.g. multiple pursuits at the same time
Added a sound engine which allows for the playing of police scanner audio
Too many back-end changes for me to even begin naming, unfortunately

Pursuits

All pursuit code has been rewritten and the new code is now split up across more than 3 different classes, each handling separate pursuit related things.
Pursuits are much more optimized and polished and it is now possible to have up to 3 pursuits running at once.

Backup and suspect AI has been worked on extensively, resulting in the following improvements:
- Cops will try to ram the suspect off the road as well as box him in
- Cops will not open fire unless instructed to do so or provoked by the suspect
- Cops will leave their vehicles and pull the suspect out of his vehicle if they get a chance
- Cops will make every attempt to arrest the suspect rather than kill him
- Police helicopters now use searchlights
- Police helicopters now fly in a much more efficient fashion
- Police helicopters will engage the suspect if instructed to or provoked by the suspect
- Suspect will do anything to escape, including running over officers, changing direction if needed, driving against oncoming traffic etc.
- Suspect may flee or surrender if their car is too badly damaged, they are boxed in or if their car becomes stuck

In TBOGT, police bikes, police buffalos and police stingers are all now incorporated into police backup
NOOSE cruisers are now incorporated into NOOSE backup

Traffic Stops

Suspects will now, in most cases, pull over to the side of the road in a proper fashion
Added an "other" option to the reason selection
Helpboxes rather than drawn images are now used for the selection menus
Added the ability to check a suspect's license on the police computer
Added big vehicle animations for trucks
Added a special set of animations for bikes
Polished up the animations with more sync
Persona system allows for up to 2 million unique names which are generated on the fly and then permanently assigned to the ped
Uses smart checks to determine suspect's level of cooperation

Police Computer

Added a police computer which can be accessed by pressing E in a cop car
Police computer comes with an LCPD database menu which can be used on traffic stops
Added the ability to call for backup through the police computer

Testing Menu

Added a testing menu which can be accessed by pressing ALT + F12 at any time
Testing menu can be used to force callouts (BUGGED), force world events and to force duty status.

Arresting

Arrest code totally rewritten to make use of all features of the new engine
Both types of arrest are now conducted by aiming at the suspect and pressing E (aim with a melee weapon for normal arrest/citation and with a gun for gunpoint arrest)
Added the ability to call for prisoner transport with both types of arrest
Added the ability to drive the suspect away with both types of arrest
Added the ability to release the suspect with both types of arrest
Added the ability to leave a suspect cuffed and return to him later
Both types of arresting are now far more simple and polished

Frisking

Changed method used to get the nearest ped when pressing ALT + R, now far more accurate
Added smart checks to determine if the ped is carrying anything or not
Drastically reduced the chance that a ped will flee if they have nothing on them
Added much more synchronisation to the animations

Callouts

Polished up all callouts in various places
(we have not added any more, yet)

NOOSE Air Support

Added a NOOSE Air Support Unit (ASU) which can be called at any time by pressing ALT + V
NOOSE ASU will fly to the player and then hover above them, scanning the area for hostile peds and engaging them
NOTE - This thing can be quite crash prone at the moment, so use it in moderation

Duty System

After pressing ALT + P, you will be informed that LCPDFR has started and will then be shown the location of nearby police stations, you will then be instructed to go to a police station to go on duty
After arriving at the police station, you will be teleported to the lawyer office interior which now serves as the police department interior and in there you may enter one room to go on duty and the other to get a partner/refill health and armour.
The police department can be accessed at any time by entering any police station.

World Events

Added a world event system which allows for the creation of random events and scenarios whilst playing
Added a pursuit world event where a police unit will start chasing a suspect, you may join the pursuit by pressing E

Taser and LTL Shotgun

Reworked the taser a little, it is now far more effective and polished
Added a less than lethal shotgun which can be used by equipping the baretta shotgun, aiming at a ped and pressing T
Both the Taser and LTL shotgun will force a suspect to drop their current weapon and become more compliant

Hardcore

Reworked some weapon damage values
Reworked damage from hits to the head, now uses a random value between 99 and 200.

Installer

Added a 'System Compatibility' check - detects whether your computer can run LCPD:FR.
Various fixes.