I still love my old AD&D books, but like an immigrant whose facility with his birth language fades with time, I have trouble reading the stat blocks of the first edition. Also, it didn't help that a lot of critical information is spread over multiple books-- creature descriptions in the Monster Manual, attack tables in the DMG, spell descriptions in the Players Handbook. As sort of an exercise, I decided to try plugging a few AD&D monsters into 4th edition formats. My intention was to consolidate in one place all the information I need at the table to run the monster, and it proved remarkably easy.
Here's one quick example. (Note that I convert AC to the "ever upwards" scale, and THACO to attack bonuses.)
AD&D Goblin in 4th ed format Show
HD 1-1; Hit Points 5
Speed 60 ft
Senses infravision 60 ft
Saves PPD 13, PP 14, RSW 15, Breath 16, Spell 16
The goblin suffers a -1 penalty to attacks while in daylight.
Spear (weapon) At-Will
Attack: melee (one creature); +0 vs. AC
Hit: 1d6 damage.
Hurled Spear (weapon) At-Will
Attack: ranged 10/20/30 (one creature); +0 vs. AC
Hit: 1d6 damage.
Alignment Chaotic evil Languages Goblin, Common
Equipment Wooden shield, 2 spears
Granted, the goblin's about as straightforward as it gets. For something like the rakshasa or malebranche devil, the block swells with summaries of their spells. Also, I found myself creating a "Flurry" line for every creature with a claw/claw/bite routine. At the very least, though, I think I'm back up to speed on finding what I'm looking for in the old format.
What was particularly illuminating about this exercise was seeing just how much of a creature's options fell under the "standard actions" heading. In 4th edition terms, everybody's action options for an AD&D round was basically 1 standard action OR 2 move actions. Knowing that makes me speculate about how 4th edition creatures might operate on a 1st edition clock...