Dreamfall has more of an impact if the player is familiar with the events of Longest Journey, but it stands quite well on its own despite the overlap.
April from the first game is virtually unrecognizable in Dreamfall, due to the ten years that have passed since the Longest Journey, so it's not like the two games flowed directly together. More like two different story lines of two unrelated characters that eventually merge into one overall plot.
Longest Journey feels like the quintessential mid-90's point and click Sierra adventure game from a game play mechanics standpoint. Very dated, but the story and somewhat clever/convoluted, point and click-y puzzles are really what make the game stand out and worth playing.
Dreamfall attempts to use late-90's style 3D controls, including a fairly crude combat system, but navigation through the game is still much smoother than Longest Journey. Puzzles are simpler with more emphasis of somewhat basic action platforming. Plot and character development again are the key strengths of the game, and the reasons why most people enjoyed it.
I enjoyed Dreamfall immensely enough to play through it again on PC (better visuals are appreciated). I actually spent more time playing this game on the 360 than any of the 360 titles I initially bought with the console (gears, bioshock, Halo 3, tomb raider...). The story was very engaging, and the characters very likable despite their human flaws.
Overall, very different games in execution, but both well worth keeping in a collection.
Best bet is to hunt down a copy of the Game of the Year Edition, which has both Longest Journey and Dreamfall. You should be able to find a used copy for $20, maybe less.
Dreamfall looks much better on a current PC with the higher display resolution. The Xbox 720x480p output looks very clean, but still SD pixelated on an HD display.
Or you can buy both through Steam ($20 or 25 for both).







