Well, much like the initial confrontation with Tuco in Season 1 (when Walt blows out the room with the magic of Science) his plans work out rather implausibly well. And, much as I loved the confrontation with his former associates, I think it'd ultimately be pretty easy for Elliot and Gretchen to wriggle out of Walt's bluff once the initial shock of the encounter passes for them.
Overall though, while the blatant effectiveness of the machine gun trick was pretty eyebrow-raising for me, the finale was very satisfying in that it certainly wasn't inconsistent with anything that came before. They even bothered to establish, via Jesse a few episodes back, that Walt is blessed with tremendous luck, time and time again. As finales go, much as Gilligan promised, 'Felina' did an impressive job of avoiding any deliberate ambiguity while tying up more loose ends than I would've thought possible in a 55-minute episode that didn't even find it necessary to eschew Breaking Bad's usual contemplative pacing. It was a very Walt-centric finale, sparing almost no time for Jesse, but his box-making reverie sufficiently made up for that I think, an odd little callback to Season 3's "Kafkaesque" episode.
A few odds and ends: http://entertainment.time.com/2013/09/30/breaking-bad-watch-say-hello-to-my-little-friend/http://www.vulture.com/2013/09/dream-of-jesse-pinkmans-happy-ending.html
I'm sure I'll find out with a little more internet surfing, but at the moment, I'm unsure of and wondering why the episode is called 'Felina' ... ?
- Walt confronting Gretchen/Elliot. The image of them tagged by red lasers as bedraggled Walt looms behind them like a phantom, admonishing them: "Cheer up, beautiful people," might be one of my favorite moments from the final half-season. This whole scene was really terrific. He has always been a dark phantom looming in the shadows of their privileged life (even if we never do get the full details of their ambiguous falling-out); here that is made manifest, and the performances (especially Cranston's) are pitch-perfect.
- Walt's close call with the police in the opening. Unique, visually interesting way of executing a moment of near-capture.
A couple minor bits I could've done without:
- The flashback to the pilot as Walt roams his house. We get it; this was totally unnecessary, a cliche trick BB usually knows better than to indulge. At least it was dispensed with pretty quickly.
- The call from Lydia at the end, where Walt explains he poisoned her. I just see no reason we needed this. Maybe a shot of her dead to confirm the poisoning worked as intended, but not a conversation.
- The final song as things close. I think BB has time and again done a surprisingly great job choosing music to use. That final song though, eh.
But nitpicks aside, I feel pretty positive about the finale overall.