Look, no offense, but should anyone really be surprised by the length of Mephiston? As someone else mentioned, the preceding two entries in the same series were of considerably shorter length than most Black Library novels. You have to take that into consideration when making a financial commitment that probably exceeded £300/$400.
If you were going to spend that money on Black Library products anyways, then Lemartes is pure bonus and any disappointment as to its length has to take that into consideration. If you spent more than you normally would have, though, then I would argue you needed to do more research.
The Talon of Horus, for instance, was the first novel in an upcoming series; Sabbat Crusade was an anthology billed as a sequel to another Gaunt's Ghosts anthology, which itself was the same length as a novel. In both cases, there was reason to expect something with substantial word count. Lemartes, though?
If you were going to spend that money on Black Library products anyways, then Lemartes is pure bonus and any disappointment as to its length has to take that into consideration. If you spent more than you normally would have, though, then I would argue you needed to do more research.
The Talon of Horus, for instance, was the first novel in an upcoming series; Sabbat Crusade was an anthology billed as a sequel to another Gaunt's Ghosts anthology, which itself was the same length as a novel. In both cases, there was reason to expect something with substantial word count. Lemartes, though?