Well, the problem with s4 is that the Klingon storyline comes across as very artificial and an excuse for Worf to join the cast. And you can tell, because in s5 we're back to the Dominion storyline that was so rudely interrupted. But TNG was where the Klingons were actually developed for the first time from their Evil McEvil TOS days, so their politics and mythology there were all new and were among the first ongoing storylines.

Heart of Glory isn't the ep with Worf's brother, I phrased that badly, it was the ep where I had my first "aw, Worf" moment. The one with Worf's brother Kurn was Sins of the Father, which also basically introduces Klingon politics and their home planet, never seen before (this was also before ST VI).

Good Klingon TNG eps for Worf development to watch:

Emissary (The one which introduces K'eyhlar, played by the fabulous Suzie Plakson; she's flippant and sexy, and you can see how Jadzia would remind Worf of her)

Sins of the Father (introduces Kurn, Duras, Mogh's backstory and Chancellor K'empec, a wily old fox - also the Klingon banishment ceremony, and because the ending for Kurn and Worf is so different you'll see why Sons of Mogh struck me as an inferior remake)

Reunion (K'eyhlar comes back, so do K'empec and Duras, Gowron gets introduced, and so does Alexander; this is the one where for the first time a Starfleet regular character does something that puts his people's ethics above Starfleet ethics).

Bear in mind Worf and the Klingons actually weren't my favourites on TNG, just secondary interests, but still, I loved these eps.