I think season 3 has been interesting in part because it's become an extended meditation on what has occurred for the two main characters in seasons 1 and 2. The first episode of the season showed a rift in how both characters chose to digest what they've done; Walt stubbornly denies his culpability in "breaking bad" whereas Jesse finds resolution in embracing a villainous persona that sometimes borders on the melodramatic. Almost instantly both strategies fail to be convincing to the audience. But the interest has been in the characters slow lurch towards figuring that out for themselves and, hopefully, figuring out how to address their own recent past in a more authentic way. You could even argue that Hank is undergoing the same process, putting a halt on his own future in order to chase down a white whale that all the evidence suggests is long gone (okay, so he happened to be right on the money, but the psychology remains the same).
Every episode has stayed consistent with that arc, in my opinion. Walt repeatedly attempts to return to his family while nonetheless continuing to cook under the table. The sterile lab allows him to remain insulated from coming to terms with what it is he's actually doing. And Jesse can't stand the lab because it prevents him from acting out; he's not evil unless he's actually on the street pushing or threatening people. The actions both characters are taking have little to do with what's actually going on but about what's already gone on in the past. And I disagree that the flashback scene with the now dead girlfriend was pointless. The conversation they had was about repetition, about whether or not the experience of the same door can be different the second time around. And in the same episode Jesse hooks up with another meth-head and corrupts her, just as he did with the previous girlfriend. The question is whether the outcome can be different on Jesse's second run, hopefully through a change in Jesse's behavior.
I could go on but yea that's generally why I feel that Season 3 has been pretty engrossing. It certainly can't stand on its own the way the previous two seasons could, and from a plot perspective it's a mess, but I'm totally loving the introspective tone paired with the occasional balls-to-the-wall crazy.