Ultimately, no. It felt like a rush job. What became the series finale was originally meant to take the show to a very dark place, and become a cliffhanger for a ninth season we now know will never be. What it ended up becoming felt more like a neat bow tacked on to an unfulfilling gift that lacked oomph.
All season long, the show has been building up a grand mystery involving LokSat that gets fully concluded in the last act, so was the final scene, in which Castle and Beckett takes bullets to the chest and gut, even necessary? Everyone knew Stana Katic wasn't returning, and it's disheartening to think this was the best the show could come up with for Beckett's end. It could have been constructed better, and more deserving of eight years worth of fan devotion.
Yes, the episode properly wraps up the show's one continuing arc, revealing Mason Woods from the Greatest Detective Agency to be the C.I.A.'s dirty analyst, but it all built to such an awkward final moment that it didn't feel like an honorable ending to the Caskett story at all. It feels like the end of another mid-chapter with a cheap ending.
The fact is, no ending would have worked. There was no winning here. Had it been a season finale, fans would have felt betrayed that Beckett was dead; with this season finale, they're left with nothing emotionally important to hold on to. The Castle writers likely felt compelled to tack on a happy ending, but we certainly wish they'd never put themselves in that position to begin with.