I picked this up a day or so ago but haven't really had the chance to play all that much of it. What I have seen, however, is brilliant. The train concept might seem weird, but the theme in general fits, and you can notice slight differences in both the environment at times and the score which show the western genre influence on the game. Very minor, but there. I imagine that most will probably go through without even noticing, which is good for those who don't like the idea.
At it's core it's a true Zelda game and a pretty awesome one at that (so far). The princess/phantom concept works well and isn't thrust on you throughout the game - just in the one reoccurring dungeon. Yes, there is another one of those, but from all accounts it fixes the problems of the Ocean Temple completely. Far less repetitive both in design and execution, no time limit, and .... well, I've only been there once so who knows? But all the other dungeons are typical Link solo missions.
One thing I did notice so far is that the control scheme is slightly refined from PH. Just little things like you no longer have to make a tiny circle on the edge of the screen to roll, but rather just tap any direction twice. The controls are still all touch screen based so keep that in mind, I know how polarizing that can be. Yet to see if the train is an improvement on sailing; I could see it going either way at this point.
All in all I'm impressed with what little I've played so far, and reviews are good - constantly praising the game as an improvement over PH. If you rock a DS and like Zelda, you should probably get on this.