I think the one of most suprising thing to new players would be the fact that in 1e an ancient red dragon (the oldest age category) would have 11 HD, 88 hit points, a breath weapon that did a whopping 8d6 damage, and a 40% chance of possessing 2 magic-user (arcane) spells each level up to 4th level - that's a grand total of eight spells.
This is running purely off of before morning coffee rememberance and not being able to check my books since they are half way across the country, but didn't a dragon's breath weapon deal damage equal to the dragons hp on a failed save and equal to half the dragons hp on a successfull save in 1e?
Also wasn't weapon damage by size of opponent a 2e thing and not a 1e thing?
And that racial limit on levels thing was always silly and didn't know people actually enforced that. =op But to each his own. =o)