LoZ: Spirit Tracks feels like Phantom Hourglass with trains.
Cole needs a suitable vessel for Malladus to arise again, and that vessel needs to be of the Royal Family. So who other than the princess of Hyrule, Zelda? Cole and Byrne send Zelda's spirit out of her body, and take it to the tower of spirits. Only Link can see Zelda's ghost, though, so he sets out to clear a few dungeons, advance through the tower, etc...
To get around the large overworld you'll use your Train. Simply trace a path through the tracks of your choice and go to your planned destination. There are only 5 dungeons in the game this time around, but the Tower of Spirits (which you return to after each dungeon) is more than two dozen floors high and therefore feels like two dungeons in itself.
In the tower of spirits you'll play as Link and have zelda assist you through a Phantom. Those who have played Phantom Hourglass will remember these hulking suites of armor as enemies; but this time you can have Zelda possess a Phantom to assist you. Controlling Zelda is a bit difficult though, as you must draw a path for her to follow or have her follow you. Using Zelda to assist you in puzzles and whatnot is quite simple at first, but in the higher floors of the tower there are some very tricky puzzles indeed, requiring you to really think.
Having Zelda as a playable Phantom is good fun and an interesting addition to the game but it's also somewhat frustrating. If you manage to get your head around the fact that Zelda's AI is that of a snail, you then have to deal with the fact that she's as slow as a slug. Whether Zelda follows you or follows a drawn path she'll walk very slowly. Let's say your walking through a corridor and you turn a corner; you haven't slowed down so zelda hasn't caught up to you. Because she's still not around the corner but you are she tries to walk directly to you, therefore walking into the wall until you come to get her. This gets annoying especially when you're backtracking to previous rooms, making you spend more time than you need to.
Another thing is that there are a number of ideas from previous Zelda titles that make an appearance in Spirit Tracks. We all know about the "Lost Woods method," where there are a number of areas that you must pass through in a certain order to get through. It's in Spirit Tracks. At the start of the game you sneak past a few castle guards, that has been done before hasn't it? It's in Spirit Tracks. What about following the correct path through the fog in Phantom Hourglass? Yep, it's in Spirit Tracks. And who could forget the temple of the ocean king? The Tower of Spirits is just like that, minus the backtracking through every floor (which is a good thing).
The game is quite easy, too. You won't often find yourself stumped over a puzzle for a long time, and in most cases it's almost like the game tells you how to solve the puzzle. The bosses aren't very difficult either; typical Zelda Bosses, where you find out how to weaken it, attack it's weak spot until it gets up again, and repeat that method 2 more times.
There are 3 new weapons to gain in Spirit Tracks, which is a good sign, as new weapons are what is expected with each zelda title. One of them being a whip, which is great fun to use, but as usual, the Boomerang and the Bow and Arrows make appearances once more. There are a lot of sidequests in the game which will give you access to goodies when you complete them, so you'll be spending time with Spirit Tracks after you complete it.
Overall, the game is a good buy, but it's too easy and too familiar for most Zelda veterans. I'll give it credit for trying something new, having very nice graphics for a DS game, having a good soundtrack (unlike Phantom Hourglass which recycled nearly every tune) and having a lengthy quest, but if you're looking for the next big thing, this isn't it. Zelda fans should hold tight for the new zelda title coming to Wii and ignore this small distraction.