At the moment the approval rate on steam seems quite good, I don't see newbies having the same tastes as your group. New players will have to cope with (for them) quite difficult zombies and a game where they know almost nothing. That players with hundreds of hours in a game and almost complete knowledge have symptoms of fatigue is normal. Happens if the game stays unchanged, but even worse when it changes away from the particular players tastes.
I'm an "old school player" (for an appropriate definition of old school, "Arcanum" and "Planescape Torment" are still in my top-5), so I don't think the dividing line is there.
But the game definitely started as a crafting and sandbox game (because some other parts like the RPG part were not fleshed out from the start) and some or many players drawn to the early versions don't recognize later versions as "their" game anymore. For me (I started with A15) the direction of the game has been almost ideal, even the (half-finished) A17 had (for me and my co-op friends) more positives than negatives.