A lot of the lore changed between 1st and 2nd edition as TSR post-Gygax tried to make their game family friendly, such as the changing of demon and devils to tanarii and something else.
Here's what the early edition grognard's from Dragonsfoot (DnD's RPGCodex equivalent) have to say:
http://www.dragonsfoot.org/forums/viewtopic.php?f=1&t=7116&p=107973
1. Ability score tables now list scores from 1 to 25 in the PHB.
2. Ability score functions changed slightly, such as weight
allowance for scores less than 10 and % chance to learn spells for scores from 10 to 16.
3. Ability scores of 5 or lower no longer limits class selection.
4. Open doors changed from a d6 to a d20.
5. Intelligence no longer affects the minimum number of spells per level for magic-users.
6. Maximum spells per level has been reduced to an optional rule.
7. Loyalty and NPC reaction changed from d% to d20.
8. Half-orcs removed.
9. Racial level limits increased and no longer based on ability scores.
10. Slow unlimited advancement for demi-humans is an optional rule.
11. Gnomes now receive ability score adjustments.
12. Racial ability minimum and maximums changed.
13. Demi-humans no longer begin knowing several languages.
14. Additional languages for demi-humans no longer limited by race.
15. Life expectancy of most demi-humans greatly reduced.
16. Dwarves now have a 20% chance for all magic items not specifically suited to their class to fail instead of a 20% chance of failure for rings only.
17. Dwarves’ underground skills have slightly different probabilites.
18. The resurrection spell now affects elves, and raise dead may affect elves at the DM’s option.
19. Gnomes now have a 20% chance for all magic items except weapons, armor, shields, illusionist items, and thief items to fail.
20. Gnomes’ underground skills have slightly different probabilities.
21. Halflings now receive a +1 to their attack rolls when using thrown weapons or slings.
22. Halflings no longer have the 20% chance for magic rings to fail when they use them.
23. Experience point requirements for classes changed, most notable is the paladin.
24. Weapons and armor permissible to some classes changed slightly.
25. Class prime requisite ability scores changed.
26. Classes were divided into four main groups (warrior, priest, wizard, rogue), no sub-classes exist.
27. Class titles removed.
28. Assassin, barbarian, cavalier, and monk classes were removed.
29. Bard and ranger classes changed entirely.
30. Fighters no longer make a number of attacks equal to their level when fighting enemies with less than one hit die.
31. Weapon specialization changed for bows.
32. The monthly income for establishing a stronghold was removed.
33. Paladins now receive four weapons proficiencies at 1st level (and gain one every 3 levels instead of every 2 levels as in the UA).
34. Magic-users now called mages.
35. Mages, illusionists, and other specialist wizards share
the same experience, hit die, and spell progression tables.
36. Mages now receive hit dice up to level 10 instead of level 11.
37. Mages no longer have the ability to construct strongholds.
38. Illusionists no longer are a separate class, but are now specialist wizards.
39. Illusionists no longer have their own spell list.
40. Cleric turn undead table changed and included in the PHB instead of the DMG.
41. Druids are no longer a separate class, but are now priests of a specific mythos.
42. Druids no longer have their own spell list.
43. Druids no longer have a class level limit.
44. Thieves now allocate a number of percentage points to each skill at 1st level and with each additional level increase to their various skills instead of having each skill increase by
the same amount for all thieves.
45. The pick pockets skill functions differently.
46. The open locks skill functions differently.
47. Thieves can now remain hidden in the shadows while making very small, slow movements; and a hidden thief is equally hidden from creatures with or without infravision.
48. Multi-class combinations allowed changed slightly.
49. Half-elven multi-classed clerics no longer require a minimum wisdom of 13.
50. Multi-classed wizards cannot cast spells while wearing armor.
51. Multi-classed priests are still restricted to priest weapons.
52. Dual-classed characters may now have up to four classes.
53. Dual-classed characters may only select one class from
each class group.
54. Alignment definitions changed.
55. A change in alignment now doubles the amount of experience needed to reach the next level instead of causing a loss of a level.
56. Additional weapon proficiencies for level advancement now start counting from 1st level instead of including 1st level.
57. Non-weapon proficiencies*.
58. Silver pieces are now 1/10th of a gold.
59. Starting funds for a mage is now 1d4 + 1 instead of 2d4.
60. Priests may not retain any starting funds after purchasing initial equipment.
61. Prices for various items, including weapons and armor changed.
62. Some new items added.
63. Field plate and full plate no longer reduce damage.
64. Weapon vs. AC type replaced with weapon type vs. armor and made optional.
65. Missile weapon range now given in tens of yards for all situations.
66. Encumbrance now calculated off of actual weight and does not include bulk.
67. Spell components made optional.
68. Spell lists were changed, all wizards now use the same
spell list. Priest spells are divided into spheres and clerics
and druids use the same list.
69. Some individual spells have changed.
70. Awarding experience points changed.
71. Training reduced to an optional rule.
72. A natural roll of 20 is always a hit, regardless of the AC of the target.
73. THAC0 for thieves and magic-users changed and is unlimited in progression.
74. Segments are removed from the combat round.
75. Initiative is changed.
76. Group initiative and individual initiative optional rules.
77. Characters and creatures with multiple attacks do not automatically attack first in the round.
78. Weapon speed now affects initiative as an optional rule.
79. Two weapon fighting is only available to warriors and rogues.
80. Non-lethal combat rules changed.
81. Parrying rules changed and reduced to optional.
82. Some saving throws now have a priority over others.
83. Magic resistance no longer affected by caster level.
84. Not all monster poisons are lethal anymore.
85. Characters now gain 3 h.p. per day of bed rest instead of 1.
86. Characters can now die if they suffer 50 points of damage
from one attack, regardless of their hit point total, if they
fail to make a save vs. death.
87. Surprise changed, uses a d10 and represents one full round
of surprise instead of a variable number of segments. Spells
cannot be cast during the surprise round.
88. Surprised characters lose their dexterity bonus to AC,
they are assumed to be totally non-reactant.
89. Henchmen are now special NPCs that the DM introduces into
the group and are friends and allies but not employees of PCs.
There is no restrictions on the level of a henchmen acquired.
90. The illumination radius of torches, magic weapons, and
other items is reduced.
81. Halflings’ base movement changed from 9" to 6.
82. Jogging and running optional rules added.
83. All characters have a 40% chance to climb walls.
94. Climbing modifiers changed.
These changes are listed in the 2nd edition PHB, even more
changes can be found in the DMG. Also, many monsters have
changed, especially with regard to THAC0, dragons are
completely different. "