There are very few shows that are fantastic from start to finish. Some take a while to get their footing, some lose their way somewhere in the middle, and others fizzle out toward the end, but it all comes down to people usually discussing their favorite seasons and declaring which are the worst. You would be extremely hard pressed to list a worst season of Breaking Bad. There are tonal shifts in the series, so you could certainly prefer one over the other, but the show never once made a misstep or felt like it was dragging its feet. It starts off strong and continues that way through to the conclusion.
The show follows chemistry teacher Walter White and one of his former students Jesse Pinkman as they create and sell crystal meth. Walter has come to the decision to do this when he finds out he has lung cancer and very little to leave his family once he is gone. As the series begins he knows everything about the chemistry and nothing about the business, and as you can imagine, he learns it the hard way. He also transforms, gaining confidence he never had before which eventually turns into hubris.
I suppose you could consider the above a spoiler, but I think the nature of the show is fairly apparent. Walt starts out becoming a kind of anti-hero and eventually turns into a villain. If that concept doesn't sound appealing to you, Breaking Bad is not your show. There are very few complete innocents among the characters, though the wrongs they commit do vary in degrees. However one of the fascinating things I find about the show is that it acknowledges that none of us are pure evil either, and can often find ways to make you sympathize with even some of the more ruthless characters. It happens most frequently with Walt in particular. As someone who sees in shades of grey rather than black and white, I like that.
The pacing of the show is also top notch. Most of the seasons follow a pattern, building tension that keeps you coming back each episode, but the climax often happens a couple episodes before the season finale. This allows you to reel a bit from the explosion and also see its aftermath, giving you just enough info to lead into the next season and wonder what will happen next. Or in the case of the final season, to wrap up nearly all the loose ends quite nicely. While there are a few elements of uncertainty by the end of the last episode, it's reasonable uncertainty, the kind of thing you can decide for yourself how they turn out without feeling betrayed by the creators.
While Vince Gilligan's vision for the show (and the choice to make it only five seasons) play a large part in helping it to feel so complete, a large amount of credit must be given to the actors involved for making the characters feel so compelling and real. I may have once thought of Bryan Cranston as the goofy dad from Malcolm in the Middle, but I'll never look at him the same way again after this. I've noticed that many of the performers are going on to future television projects, and that makes me happy. They are fantastic talents and deserve everything they get.
The only problem I have with the show is a section of its fans. This is a pretty normal problem, I suppose, as whenever people start to get fanatical about something, there's always going to be some of them that take it too far and cross a line. In this case, where you have a character who has become a villain, it is a particularly disturbing line. Basically, no matter how despicable Walter's actions become, these people still side with him. I can understand this to an extent. I found myself frequently wishing for Walter to come out on top whenever he found himself in trouble. But I also found myself completely horrified by some of his actions, and my sympathy always sided with those he put down in the process. As I watched the finale, I occasionally cheered out loud as I saw people take a stand or otherwise become triumphant. None of my cheers were for Walt. At best, he earned a smirk. I was happy with what he accomplished by the end, but I also could not truly consider him the hero of the story.
Obviously, I'm doing my best to not post spoilers here, as I want to give everyone a chance to experience the show and its twists as freshly as possible. However I also can't help but think that even if someone knew all the big reveals at this point, they would still enjoy watching the show immensely, because the execution is so strong. I knew all the big deaths before I ever started watching Buffy the Vampire Slayer, for instance, and they still hurt because they were done in a way to make you feel it. I think the same holds true for Breaking Bad.