There's little to say about the mechanics. Back to the Future The Game: Episode 4: Double Visions
uses the same system as previous episodes. The camera is finally fixed and not an issue and the node-navigation system has once again proven itself as the best control method, especially in Doc's crowded lab.
After the stellar Citizen Brown, Double Visions is a bit of a letdown as far as puzzle gameplay goes. Nearly all of the puzzles are of the "Get this object for this person" variety. There's a really neat sequencing puzzle using Doc's mind-mapper device, though most of the puzzles felt like I was everyone's errand boy. There's some connection within the story - so nothing feels out of place - though it's a major step down.
Doc's mind-mapper is one of the best sequences in the game yet and resembles the "word hint sequence" puzzle from Doc's lab in the first episode, which I liked. Without going into spoiler-y details, you have to use objects in the environment to affect a test. It's cool, especially if you decide to go for the related Trophy. I really wish there were more puzzles like this rather than the fetch quests.
Double Visions is an interesting episode, though only for how it foreshadows what's coming in the next episode. This is the first episode where I really wanted to jump into the next episode based on the epilogue. The actual gameplay, however, is a big letdown and feels a bit like filler material.