I would say that What Is To Be Done? is one of Lenin's most important works, if anything I'd say it's underrated. Like (mostly) all of his works, it talks directly about the situation in Russia at the time, but that doesn't make it any less useful. You just have to extract the universal principles from the tactical particularity he's writing about.

WITBD? focuses on the need for organizing, and not just any kind, but actual revolutionary organizing with both theory and practice, for bringing together the proletariat with all other revolutionary classes and even individual intellectuals. It speaks against just focusing on a binary interpretation of class struggle (proletariat vs bourgeoisie), and instead it tells us to focus on any struggle that is revolutionary (anti-colonial struggles, gender liberation struggles, etc.).

Here's how Losurdo describes it in Class Struggle: