We know Walter has something planned; we just don’t know what. We know he’s wearing a similar color and style of shirt that he wore when he defeated Gus Fring. We’ve seen him building some contraption while singing along to a song about a man hiding in New Mexico out of fear of retribution for a murder he’s committed. We know he’s picked up some serious weaponry, both mechanical and chemical. When it happens, just as it did with Tuco and Gus, we’re faced with a mixture of “OMG” and “but of course.”
It’s almost anticlimactic. In fact, you could make the case (and several people have done so) that “Ozymandias” is the season’s climactic episode, and that in a Shakespearean five-act structure season 3 was the series’ climax, and this is all denouement. Just really bloody riveting denouement. The groundwork has been laid so meticulously that an ending like this is expected, yet when it happens, it’s still a huge “oh sh*t” moment. The moment Walt pushes that button, the feeling of being given what you want, seeing someone killin’ Nazis, is hard to not enjoy to bits. That he saves Jesse in the process, who gets to exact the ultimate revenge on Todd, is really, really sweet icing.