Sometimes I like the original better...
I liked the first Monkey Island game the best. My second favorite is the 3rd in the series.
I liked Syberia a lot better than Syberia 2.
I liked the first 3 Myst games better than the last two. I find it hard to say which of those first three was better because they had different strengths.
The first Tomb Raider is my favorite and I like it WAY more than any of the others.
Riddle of the Sphinx was better than Omega Stone as a game, though Omega Stone had a lot of technical improvements.
Despite a few pixel hunts, I liked the first Gabriel Knight game the best overall. It had the best interactivity.
Runaway was better than Runaway 2.
Dracula Resurrection was better than Dracula Last Sanctuary.
As an adventure game, The Longest Journey was WAY better than Dreamfall.
7th Guest was better than 11th Hour.
Shivers was better than Shivers 2.
On the other hand...
In most ways, Atlantis II was better than Atlantis I.
I liked Schizm 2 better than the first Schizm. The puzzles were too tough for me in the first one. I'm not sure which is the better game though.
I liked Zork Grand Inquisitor. It's hard to compare it with the early Zork text games, but it's also better than the first graphical Zork game, Return to Zork.
King's Quest 6 is definitely better than King's Quest 1.
Nancy Drew 1 and 2 were the worst ones IMO.
The first AGON game was not the best one.
My favorite RHEM game is the second one.
The first Agatha Christie game was not the best one. I think Evil Under the Sun is the best one so far.
Under a Killing Moon and Pandora Directive were better than the first Tex Murphy games, Mean Streets and Martian Memorandum.
So far my favorite Sherlock Holmes game is Silver Earring, despite that loudmouth dog. Of the earlier Lost Files of Sherlock Holmes games, Rose Tattoo was better than Serrated Scalpel, if only because it had full sound.
Day of the Tentacle was better than Maniac Mansion.
I think Indiana Jones and the Fate of Atlantis is the best Indiana Jones game. I think it was the 3rd Indiana Jones game -- certainly not the first anyway.
Egypt I (Egypt 1156 B.C.) was much worse than the later Egypt games (Egypt II: The Heliopolis Prophecy and Egypt III: The Egyptian Prophecy).