From 1.07 to 1.18.

Programming fixes

   Assorted tweaks to AI code to improve AI responses in a variety of situations.
   Fixed rats squeaking after they have been killed.
   Made ropes easier to climb.
   Fixed a bug in doors that could send you skidding off or let you stick your head through a door.
   Tweaked mines so that they interact with the world more realistically.
   Fixed a turret bug that prevented a couple of turrets from working correctly.
   Increased maximum sound channel usage to 24 channels and reset default to 12 channels.
   Modified frog combat behavior so that they no longer just sit still for several seconds looking around before they become active.
   Improved the effectiveness of using your sword to block blows from your enemies.
   Set gamma levels to default when playing back movies so they look better.
   Fixed a crash that happens if you hold down a key which changes screens while mouse clicking a button to leave that screen (yes, some people will try to do this).
   Fixed a remote camera bug that effected Nvidia-based video cards.
   Added support for audio cards that only support EAX 1.0 

Design fixes and improvements

Interference

   Made several aesthetic improvements to the level.
   Made a few AI tweaks.

Shipping and Receiving

   Tweaked AI patrol routes for better gameplay.
   Add more Garrett voice overs.
   Tweaked some of the puzzles on this level.
   Added a few more powerups. 

Framed

   Added a few more powerups.
   Made several aesthetic improvements to the level.
   Added more voiceovers.
   Swapped out some spiders for some rats.

Ambush

   Tweaked the map to make it look better.
   Changed some guard models for better diversity.
   Added more conversations.
   Adjusted some difficulty settings.
   Added a few more powerups.

Eavesdropping

   Made it easier to find enough loot to achieve mission objectives.
   Tweaked difficulty settings.
   Added more powerups to mission.
   Made several aesthetic improvements to the level.
   Improved sound propagation throughout level.

Bank

   Made several aesthetic improvements to the level.
   Improved sound propagation throughout level.
   Added more Garrett voice overs.
   Tweaked difficulty settings.
   Improved lighting.
   Fixed some map bugs (added a new map page).
   Minor bug fixing.

Blackmail

   Tweaked powerups and loot available in mission.
   Tweaked AI patrol routes for better gameplay.
   Fixed a bug that if you kill some of the guards before they have an important conversation the mission was left in an unwinnable state but you didn't fail the mission.
   Added a few more loot puzzles.

Courier

   Fixed some lighting bugs that made it look like you were standing in shadow when you weren't.
   Improved sound propagation throughout level.
   Tweaked AI patrol routes for better gameplay.
   Changed some guard models for better diversity.
   Added a few more powerups. 

Trail of Blood

   Improved sound propagation through the level.
   Made some loot easier to find.
   Made several aesthetic improvements to the level.
   Tuned difficulty levels.
   Tweaked some AI patrol paths for better game play.
   Tweaked lighting to add more hiding places.
   Put more powerups in the level.

Life of the Party

   Made several aesthetic improvements to the level.
   Snuck in some more rooftop architecture.
   Tweaked some AI paths.
   Tweaked the fog settings.
   Tweaked sound propagation.

Precious Cargo

   Tweaked lighting for better stealth experience.
   Tweaked the mantling puzzle.
   Fixed a bug where you could play through mission and not trigger an important objective change.
   Tweaked sound propagation.

Kidnap

   Added some powerups to mission.
   Fixed a bug in one of the conversations that
   Caused it to repeat each time you trigger it instead of playing just once.
   Made some scrolls easier to find.
   Made some lighting tweaks to make it easier to sneak by certain places.
   Tweaked some AI behaviors to make them better responses to possible player interactions.
   Fixed a couple of little map bugs.
   Tweaked difficulty levels.

Casing and Masks

   Made several aesthetic improvements to the levels.
   Tweaked some AI patrol paths for better game play.
   Added some more powerups to the level.
   Made some lighting tweaks to make it easier to sneak by certain places.
   Fixed a couple of physics bugs that caused some objects to act strangely.
   Fixed a couple of map bugs.
   Hid some secret doors better.
   Fixed a model problem with some clocks that caused transparency problems.
   Made it so that a container for an important quest item appears in different places on different difficulty levels for increased re-playability.
   Fixed a bug where getting a mask did not always trigger the objective complete for it.
   Made some tweaks to improve gameplay.

Factory

   Made the text on the map easier to read when it is highlighted.
   Added a map page.
   Made some tweaks to improve gameplay.
   Made aesthetic improvements to the level.

From 1.18 to 1.19

This is the important parts (i.e. not to do with DromEd) of the patch notes for 1.19, which themselves claim to be just "a small sample of fixes/changes".

Renderer:

- Added windowed mode - Added single display mode option - no resolution change between menus and game - Added ingame support for all common resolutions, including widescreen - Added support for 32-bit color - Textures can now be automatically promoted to 32-bit, improving quality and effectively eliminating the palette limit - Added UI framerate cap option to avoid GPU fan spinning up in UI - Added DDS/PNG image support - Added full 24/32-bit TGA/BMP image support - Increased the maximum number of frames allowed in animated textures from 20 to 99, and increased the allowable filename length for animated textures (before the underscore) to support more than 7 - Animated texture rate can now be specified via a material file for that texture - Fixed a bug where Transparency property didn't (correctly) apply on objects that contain transparent polys

General:

- Replaced video player lib with an FFMpeg based one to play cutscenes. LGVid.ax or other codecs are no longer required - Option to use OpenAL (if available) instead of DirectSound. Includes support for audio effects in Windows 7 without an EAX-enabled driver (e.g. ALchemy) - Added "head_bob" config var to control amount of head bob - Added mousewheel support to options menu - Fixed player ground contact tracking when walking off an object (caused footstep sounds to get "stuck" on previous material) - Fixed sound cap per schema type bug and upped max sound channels to 48 - Changed screenshot output format to BMP and also added support for PNG screenshots - Changed mouselook sensitivity to be resolution independent - Added check to avoid trying to open files with reserved system name like com ports - AIs now breathe from their head instead of their stomachs. They will no longer drown when up to their waist in water. - Lowered player crouch height by a tiny fraction so he's less likely to get stuck on 4 unit tall spaces - Added better support for binding actions to the mouse wheel (can bind wheel up and wheel down as separate actions, with modifier key support) - Fixed star rendering - Added "log_player_pos" command that dumps current player pos to log file (when enabled) - Added the ability to detach from ladders by crouching - Improved mantling a bit and added optional new mantling algorithm with lower failure rate - Fixed a bug which limited number of sound channels to 16 even if more were selected - Fixed a bug that sometimes caused doors to float away into infinity - Fixed (or at least greatly improved) a bug with edge triggered OBBs sometimes failing to detect collision (in particular for slow moving objects) - Fixed framerate dependent speed issue for camvators/moving terrain (with collision type: none) - Added "fixed_star_size" option for resolution independent star size - Fixed some bugs when attaching to a ladder from water. - AIs who are facing very close to a wall will no longer turn to face south when the game begins - Health bar drawing adjusted in widescreen - Added option to fix arm rendering - Added AA to rendering of loadout screen items - Fixed pickpocket count bug that would always show 1 more maximum pickpocket than there actually was. - Added "Blocks frobs" property, allowing objects to block frobs of objects behind them (e.g. to stop frobbing items through safe doors) - Added option to left-align map notes text - Made navigation of map/objectives screen a little bit more in-game friendly (screen can also be closed with space, arrow key navigation and return to switch map/obj)

Later changes

It doesn't seem there were any more critical changes from 1.19 to 1.22, but here is the reference if you want to see for yourself:Thread on ttlg.com forums