BB had already run through its full body of ideas by the end of Season 1. Everything else was just upping the ante, writing Walt and Jesse out of increasingly preposterous contrived close-calls, and flirting with the racial/immigration subtext from various angles before abruptly writing in "neonazis as ultimate villains" in order to avoid going any further than mere flirting.
The show was good! The Wire, Sopranos, Band of Brothers are all better.
It's not that Breaking Bad wasn't a very good series, but its "nemesis" episode relied on the relatively late introduction of neo-nazis rather than unfolding as a result of decisions taken in the larger narrative, plus it was undercut by Walt's heroic exit in the finale...