The Siege of Mersadie Hive was a custom scenario lovingly crafted by Arthur. As such, unless your GM is planning to borrow the scenario by hacking together what they hear on this episode and the notes on Arthur's blog, there's really no spoilers to worry about.
As always, be aware that the podcast is not really family-friendly, and features some background noise, if that sort of thing bothers you.
In this episode, Nikolai is very briefly awesome, but is undone by a NPC's Fate Point. Luckily, the librarian is around to annihilate the archon with Smite before she can gut him. In fairness, this would have happened whether or not the archon was stunned. Librarians are, as they say, sick OP... I still think the awesome counts.
As I've mentioned (interminably) before, I haven't had a huge amount of mechanical success with Nikolai. Ironically, in this episode he kicked a fair amount of ass by dint of several spectacular heavy bolter rolls. I'm pretty sure this is the most he's ever achieved in a combat. But then, heavy bolters are also sick OP.
I know the corrupt aristocracy plot is a bit of a 40K cliché, or indeed a general cliché, but I for one have no problem with tropes emerging in my genre games. That's kind of the point. While a game about the complex bonds of brotherhood between teenagers granted enormous power but condemned to expend it in eternal war, unfolding chiefly through social interactions between missions and the decisions made during a battle, and dealing with indoctrination, loss, humanity, compassion, and the trade-offs between preserving humanity and the ruthlessness demanded by the enemies they face, could probably be quite interesting, that isn't what I'm looking for when I sign up for Deathwatch. It's particularly true because it's a very specific setting, not some generic sci-fi game where there's more free reign.