First of all, thank you for kind words. The games had their flaws, but there was something that made you return to play more.
Here's a short rundown on pros and cons of various games in the series. New features were carried over to later games of course.
ToW1
+ Has more units, maps and scenarios that all subsequent games combined
- Infantry can't enter buildings
- Graphics are OK for a wargame, but look more dated obviously
- Interface overlooks (like you could select only a couple of dozens units at once)
- Impact and armor penetration routines are simple compared to ToW2 or ToW3, which led to errors in some cases (for example, a penetration where the armor should have stopped a projectile)
ToW2 Africa + Centauro DLC
+ Nicer graphics (HDR, ambient occlusion)
+ Infantry can enter buildings, but 3D means you could see the AI limitations in tight situations (more below)
+ More accurate impact calculations like projectile normalization, advanced ricochets, advanced projectile path modeling inside a vehicle
- Hardly any trees or foliage since the game happens in desert
ToW2 Kursk + Caen DLC (my personal favorite)
+ SpeedTree foliage
+ F4 invokes a detailed damage overlay which shows all hits and penetrations as 3D vectors (a feature I proud of since it was me who pestered lead designer long enough to include it to show off how detailed the calculations are 'under the hood')
+ Skirmish mode (you can enter parameters like time of day, enemy type and strength, available support and play a generated scenario) in addition to existing scenario wizard and advanced editors
+ '2d wargame mode' - a camera mode that lets you see the battle in top-down perspective
+/- Initial stage of Kursk battle and document-based engagements (more
here) means that Germans are almost always attacking and Russians are almost always defending. Caen battles were more variable though.
+ Persistent roster (you can view your entire staff, thousands of people, at the start of the campaign instead of getting small portions of new units for each mission)
+ You can rename units and soldiers, hear gun sounds in encyclopedy, other minor improvements
ToW3 Korea
+/- Has strategic map mode, but it's simple and not everybody liked this change
+/- More modern setting
+ Completely new frag and explosion damage calculations simulating ground cover on a whole new level (you can read my short article about it
here)
- Pathfinding bug that wasn't eradicated completely (units may choose strange paths to move when you played for a prolonged amount of time or loaded a saved game)
- Not enough maps were made in time, so you may encounter the same tactical map in another part of Korea
That's basically it. I would suggest getting the game(s) on Steam. On large Steam sales you can get 50% off usually (or more if it's a special sale of a game).
You may wonder, for example, why infantry couldn't enter buildings in ToW1 while other wargames of that time had this feature. The answer is simple actually - perfectionism (BTW, did you know that all insides of a particular tank like engine, transmission, crew members, bulkheads are placed true to life in ToW series)? All (or almost all) other wargames modeled a house like an abstract semi-transparent entity. Infantry inside would simply get a bonus to their cover parameter and have a better firing position if they are on higher floors (if a wargame modeled floors). On the other hand, ToW lead designer wanted to do everything properly. In ToW2, when house interiors appeared, the houses were actual houses with doors and windows (but only one floor because of path-finding limitation). A soldier could see only what he really could see through the window. This led to a mound of problems - they couldn't see an enemy or get a clear shot most of the time. The fact that there were performance problems (see below) made things worse - each soldier AI could 'recalculate' what is happening and ray-trace what he can see now every several seconds, otherwise performance impact was too severe. That led to stupid behavior when an enemy soldier could run into a house and quickly kill a couple of defenders before they could react (it happens in real life too, but since its a game, it looked like an AI glitch).
I think that Close Combat series (2D real-time wargame) approach was the best. When an enemy squad rushed into a building occupied by your squad, you could only imagine what is happening there (tiny sprites symbolizing soldiers moving inside a house, grenades going off, cries and shots). Very atmospheric. Your imagination is and will always be the best video card in the world, so you felt like everything that was happening was right. If a soldier sprite stopped in the doors for no apparent reason (AI glitch, for example) and got mowed down, you automatically imagined that he hesitated, or stumbled, or anything. That's why soldiers there left like real people. On the other hand, in ToW, where everything looked like as is and you could pause the game anytime to assess the situation, you immediately noticed any AI glitch clearly in 3D. Your imagination could no longer hide a dumb behavior of AI in a particular situation from you, that's the price of seeing the action close up
To summarize, the series offered some unprecedented features at that time (some of them are still unique because hardly any developers are making something as deep as company or battalion combat simulation today), but these features limited the game in other areas. 2x2 km playable area with lots of units meant very stressful path-finding routines, especially for mostly one core CPUs of 2007 (the engine could used up to 2 cores). Real-time ballistic and impact calculations of 200+ units firing at once didn't help to get a higher FPS either. The fact that ToW engine was based on Il-2 Sturmovik engine that was written in Java meant that the simulation was a memory hog (the whole idea of a Java-based game was very questionable I'd say, it plagued Sturmovik games, which were very successful, as well). It was like, let's say, trying to make an almost perfect company level engagement simulation with a less than perfect engine, so compromises (less units, longer unit reaction time) were to be made.
To my knowledge, the only tactical wargame series with similar realistic approach still being developed today is Achtung Panzer series (and Combat Mission probably, but I haven't heard if they are developing a new installment). It's from a different team, and they use a different approach. When in ToW you could control almost anything, including selecting a next round to be loaded into a tank gun if you want, in AP your role is limited to general instructions like in Close Combat series. The graphics may look ugly, but they are gritty on purpose like one of the developers said. Interface is also can't be called intuitive, but it's an interesting experience to try overall. An experienced team as well, they made tank simulations Steel Fury and Steel Armor - Blaze of War.