Idk, what broke me into leftism was "Wage Labour and Capital" and what sealed the deal was "Socialism: From Utopian to Scientific". It wasn't the freshness of the ideas that blew me away but how solid and rigorous the foundations are.

Before that I thought lefties just turn the "social programs" dial to 11 and the infighting was about how to best turn that dial and how social programs should work. To see such a rigorous approach to politics blew my socks off and broke with all my preconceived notions.