Monkey Island put it best: Yes Myst is pretty, but egad is it dull! Contains Spoilers
Atrus once again invites you to one of his ages (The same one as you start on in Exile). It takes place a long time (about 10 years I think) after Myst, and Atrus' and Catherine's daughter Yeesha has grown up. Atrus has found a way to link back to the ages he trapped his sons in, and asks you to check on them to see whether or not he can release them. He goes to another age, Rime, Catherine is away, and naturally chaos ensues.
Unlike the previous installments, you start this game with tools. You have a camera and picture viewer, and later you get Yeesha's necklace that shows you events that have happened. This can be quite useful as you can take photos of the crystal viewer codes, and any maps that you find lying around. The viewer is slightly awkward, as it is hard to view your pictures outside of the game (some of the views are amazing, so this is sad) and it can be a bit laborious switching between the viewer and any puzzle you are attempting. I found it easier to copy down the information or code on to paper, as I used to with precious Myst puzzles, but this renders the picture viewer somewhat useless! The necklace is an interesting addition, as it shows you clips and fills in background stories, but on a pedantry note it is inconsistent in the way it works; for instance it shows Yeesha being chased but to preserve the story it doesn't show you who, but at other times it shows you from the perspective of the person carrying out the action, usually Yeesha as she is wearing the necklace. It is a useful storytelling device however, and enriches the storyline.
As usual, the scenery is beautiful, and the movement sequences blend much more seamlessly with the pre-rendered backgrounds. At some points you can follow Yeesha around the compound, and in some cases her actions change depending on your actions. The music is immersive and ethereal in places. I don't know if it is composed by Robin Miller as in earlier games.
The puzzles are fiendish in some places, particularly in Sirrus' Spire age. I have to admit that I gave up on his crystal resonance chair. I looked at several walkthroughs and couldn't get it to work for the life of me. If a puzzle isn't doable even after you see how it is completed, I think that counts against it. Generally the puzzles were more arbitrary and difficult to work out. On Exile it was obvious how the puzzles worked, and they had a kind of logic to them (it was a teaching age), but here buttons weren't obvious, some viewpoints were difficult to reach. The hand grasps at air or taps, but it doesn't obviously change when you can interact with something. This makes the game tedious and frustrating. The same for where you can walk to. It seems arbitrary where you can and can't walk, and its only because they made the backgrounds pre-rendered again. Zip mode only works in some places, particularly on the home age, which again, is very frustrating. You can't zip from the observatory to the linking books for instance, despite the fact you can walk from one to the other at all times. It makes no sense at all, and the snapshots that represent the zip locations are unhelpful at best.
The story is about as in depth as any of the Myst games from Riven onwards. You find out more through journals, and by looking at the ages as you walk around. The necklace also adds depth to the characters, but honestly it wasn't necessary in the previous games, and I don't think it added anything here. One of the selling points of Myst was the strange emptiness, and while I appreciate that it was because video footage looked terrible at the time, and made files huge, it didn't need to be made into a weakness just because the games are more advanced. The acting in Myst is fairly hammy, particularly from Rand Miller, so I think the less the better. The necklace just made it feel like they couldn't put across the story of the game as well as they used to. It is a minor issue however, as by and large, the game is the same as all its predecessors. The story has closure, and if you are a big Myst fan, especially of the books and surrounding world, then it is well worth playing. It is not a user friendly game, and parts will leave most people frustrated, but there are many well written walkthroughs, and failing that, the endings are on youtube.