Expert is NOT for everyone.
I've customized the Rockband 2 Fender with a new strummer using cherry switches rather than the "hair" trigger it had before.
I'm pretty hardcore about these games, for an old man.
So I just played through a big chunk of the game on Hard. Nothing jumped out at me till Master of Puppets which had a lot of very odd notes that were NOT hammers and would kind of trick me. Was a struggle to 5 star it. I went back and tried it on Medium and it was easier but still very strummy. Felt like they did a good job of keeping you entertained and feeling like you are really playing the song on Medium but I think that it is likely closer to the GH3 difficulty rather than the GH:WT difficulty.
I think, owing to the nature of the music being played it's just plain hard.
Other things I noticed. Hammers are really picky when they are far apart but the same sloppiness is allowed (as in GH3 and especially GH:WT) when they are really tight/fast. Due to this window changing size so much I found myself regressing to when I used to strum everything including HOPO's.
"Story" for single player is at least slightly more substantive than GH:WT. You start as metallica with For Whom the Bell Tolls and The Unforgiven, then a cartoon about "Metallica JR" your band with a front man you pick or design (Lars Umlaut woo) that wants to open for Metallica. You go to an open audition with Metallica but the devil guy from GH3 beat you there and has signed up a sort of 80's hard band but the power of your rock wins James Hetfield over and he gives you the devil horns for a thumbs up. Later the devil returns and tries to force his way back in with his contract from earlier, fortunately James has a picture of him crossing his fingers behind his back while signing... Pretty good stuff, not quite the feast that was GH3 but more than the famine that was GH:WT.
Progressing through the story/setlist is really easy as you basically have to get 10 stars to open a tier and each tier is chock full of Metallica and Guests. You can even sit in the early tier and play them all through to unlock later tiers. Makes it really easy to plow through to deep tiers.
When you beat a song you can get extras about it. Metallifacts, where the game plays itself and little pop up facts appear. Lyrics and sometimes videos and such too. So far I've unlocked Lemmy from Motorhead and one of the rockers from GH:WT.