I really get why Straight Silver is one of the least popular GG books, but I'm always confused by people not liking Blood Pact, which is hands-down my favourite book in the series. I really love the way Abnett writes Chaos, though, so maybe that has something to do with it.
Anyway, I finished The Warmaster, and I liked it, I thought it was worth the wait. I wasn't just being flippant about Anarch being "part 2", though - while I understand this arc is a 4-book whole, this absolutely feels like "Urdesh pt.I". That's not a bad thing, but it's something to be aware of going in, I think. It's far and away the least self-contained book so far, seeing as how a lot of its big plot threads are cliffhangers.
Anyway, I'm not sure how much the pre-Urdesh part of the book has been discussed, but that's way up there with my favourite battles in the whole series. I'm generally starved for good ship-related content in 40k novels. (Props to the related short Killbox for establishing that the Armaduke has enormous heat sinks, which has finally ameliorated my years-long disgruntlement over that one description of a ship running its conduits onto the outside of the hull to cool them via contact with space)