In my quest of learning about Dragonlance setting I came upon an adventure module set in D&D 2nd edition and now I am curious about what the previous editions were all about. I have tried to look for information on the google, but failed to find anything worth mentioning.
Core Rules Classes:
Hit Points and Hit Dice:
To Hit & AC:
Attributes & Attribute modifiers:
Magic and Spells:
Experience and Experience Points:
I think (and this is just a guess) the basic mechanic changes resulted from a change in orientation with regards to the kind of experience developers were trying offer. The following is just my guess based on perceived emphases in the games through the years.
If I recall correctly, DnD Basic developed out of a tabletop war-game. This meant simplistic rules, simple rolls, and two dimensional characters. A fighter was a fighter; an elf was an elf; etc. The goal was simple: go into the room, kill the monster, get the gold. From there, modules added narrative. Overtime, the focus began moving away from kill/loot/rinse-n-repeat to narrative immersion.
Out of this seems to have come AD&D. No longer was the simple system able to contain the diversity narrative demanded out of players. They needed more ability to customize characters. More spells. More weapons. More classes. (Dragon Magazine really helped here.) The proficiency system allowed players to choose skills beyond what their classes allowed their characters. And not all classes were created equal. Some classes needed high qualifications, like the Paladin, Monk, and Ranger. Only the best stats could qualify for the superior classes.
Interestingly, the players' emphasis on "character" rather than "level" seems to have come out in the general rejection of certain later rules (and this is based on what I vaguely remember from Dragon Magazine letters). For example, in the survival guides (Wilderness Survival Guide and Dungeoneer's Survival Guide), we found rules for such things like jumping. In short, the higher the level the greater jumping ability. Players seemed to reject it because it simply didn't make sense within the context of narrative character development. What does level have to do with the ability to jump farther? Back then, I don't believe that players saw levels as connected to or a reflection of a character's personal development.
The emphasis in AD&D on narrative immersion seems to have increased with the popularity of the Draganlance Saga. I seem to recall that the Chronicles and Legends even hit the NYT Best Seller list. Players wanted to participate in something like that. The game and its mechanics were simply changing to adapt to that demand.
I argue that video games and MMOs changed the demand again. I believe that 3.0 was an attempt to start to capture some of the feel that video games gave players. I sense that there is more emphasis on leveling up in 3.x than there was in AD&D. Note that leveling happens quicker. And when you compare powerful NPCs in their AD&D versions and their 3.x versions, the AD&D version seems to be of lower level. Ninth level used to be "name level" (go get that Wizard tower, castle, or guild and bring in followers); in 3.x the equivalent may be 15-20. Apparently, players came to accept that everything was tied to levels. The skill system ensured that anyone of any significant skill would necessarily be of a higher level (hence, the need for NPC classes).
Gear received a new emphasis and became more readily available. No longer would one have to find the magic weapons and armor on adventures and questions. They could just take their gold to the market and pick up whatever was available. Players felt higher level character with enough gold were entitled to better gear, and the system was built to accommodate that.
With the move away from narrative character development toward MMO-like leveling adventures, we saw a move back to equalizing characters of equal levels. One no longer needed to have sufficient stats qualify to be a more power class. All classes were of equal power, accessibility, and advancement difficulty. Balance became more important. Now, the main way characters became special was to become more powerful through levels so that their skills could improve and they could enter a prestige class. (Note: one could argue that the skill system allowed for more customization than the AD&D system; I argue the opposite, that characters were more customizable through the diversity of classes.) The system (now influenced more by MMOs) was starting to move back toward the simplified D&D Basic, which was based on tabletop wargaming.
And, if I may move beyond the original question, what about DND4? Well, I don't play it. I don't have any interest, so someone else would have to answer that. From what little I've seen, though, it appears that they've really tried to turn the tabletop RPG into a tabletop MMO. If so, it brings us full circle: a version based on a wargame.
Another big difference (to me at least), between DnD2 and DnD3 was the loss of "historical gods and monsters". I remember I used to go through DnD2 monster manuals looking up different Egyptian and Norse gods and associated mythological creatures. The various "default" game worlds seemed to be based on Earth's mythologies, and not these entirely new worlds.
Having played both versions, 3.x got rid of my 2 big hatreds. 1) THAC0 (defined below), and 2) no more "do I want a big or a little number?"
Task: Lift the portcullis to escape the castle. 2e: Roll a d20, if it is below your Strength (and the portcullis's weight is less than your Strength's bend bars/lift gate stat), you succeed. 3e: Roll a d20, add your Attribute bonus/penalty and compare to the target number.
Task: Putting the pointy end of a sword into the bad guy: 2e: Do you have proficiency in the weapon (or weapon group)? Roll against THAC0 (To Hit Armor Class 0). You roll d20, subtract the roll from THACO (so a roll of 19 and a THAC0 of 15 = -4). if you hit an armor class smaller than the targets, you hit. 10 is an unarmored human. IIRC, Plate mail is either 0 or 2 AC. 3e: Do you have the appropriate feat to use a sword?, Roll d20, add your attack bonus, compare to the target's armor class. Bigger number wins.
Task: You get hit by a dragon's breath, and don't want to die (you could choose to not save vs. a spell effect). 2e: Roll d20 vs. Breath Weapon. 3e: Roll d20, add your Save (Reflex or Fortitude based on circumstances), compare to the DC of the breath effect.
In 2e, you had Proficiencies instead of most skills/feats.
Weapon Proficiencies were awarded based on your class. Fighters got more at first level and earned new proficiencies quicker. A proficiency was for a single weapon type (long sword, quarterstaff, etc). In the Fighter's Book, they introduced the concept of broad and narrow groups. For example, a fighter could devote 1 Proficiency slot to longswords, 2 slots to the Long Blades Tight group (Bastard Sword, Katana, Longsword, Scimitar, 2-handed sword), or 3 slots for the Blades broad group (Bastard Sword, Cutlass, Dagger/Dirk, Katana, Khopesh, Knife/Stiletto, Longsword, Main-gauche, Rapier, Sabre, Scimitar, Shortsword/Drusus, 2-Handed Sword, Wakizashi). Non-fighters could NOT take groups as I recall. Fighters could also devote proficiencies to fighting styles. You had Single weapon, Weapon and Shield, 2 Weapon, and 2-Handed Weapon styles. They typically gave you either +1AC, or +2 to hit, or minimized weapon speed.
Outside of combat, you got non-weapon proficiencies. Think something similar to the Knowledge, Profession, and Craft skills in 3.x. Some that I recall (I'm away from my books at the moment) are Fire-building, knot tying, cooking, weaponsmithing, etc.
Another big difference is that different classes advanced at different rates. I once played a game where the DM gave us "starting XP" of (I think) 200,000 XP. It caused my fighter to be level 9, a Thief to be level 11 (I think???), and the cleric was a third level.
If you want to convert a 2e mod into 3.x, I'd start here. Personally, I'd take all the setting stuff and just redo the stuff with 3.5 monsters/stats.