In the supporters' camp we have such reviews as the one that appeared on The Founding Fields website, which give Liberator a respectable 7.2 out of 10.
In the dissenters' camp we have reviews like this one that's appeared on Amazon:
`Liberator' is a rather unconvincing story of an element of a loyalist Space Marine squad who turn traitor. The reasons themselves are rather forced and the characters quite weakly drawn. I also found some of the terminology felt borrowed inappropriately - Nova Terra is the setting but no reference is made to whether this is the planet at the centre of the major schism in the setting (Nova Terra Interregnum in M35), a quoted Inquisitor has the first name of Gideon which is the same as Ravenor's first name and one person's title is Iconoclast which is the same as a Chaos Destroyer ship class. These are individually minor points but they do create a composite view that the author is lifting names lazily. The story is not helped by being told in semi-reverse either. On the positive side it is good to see the Iron Knights Chapter appear and their names at least are consistent with their appearance in `Tower of Blood' (Best of Hammer and Bolter Volume 1). I rate this as 2 stars.
I take issue with 'the author is lifting names lazily' bit. I believe the names I have used are appropriate, given the context (and who ever heard of more than one person sharing the same name?), but you'll need to read the story yourself to see why. As to the reasons why the characters fall to Chaos... that was already in the Chaos Space Marines Codex.
But those points aside... 72% or 40%? You're just going to have to read the story yourself to decide which is the fairer review.
You can pick up a copy of Treacheries of the Space Marines here.
PS - In case you hadn't noticed, I'm invoking the 'Black Library fiction as tie-in fiction' clause today.