I'm not at the point where I can say "I can't express how impressed I was with this episode," but I did find myself pretty pleased with it. It's definitely one of the best episodes of the series so far, though I don't know if I'd necessarily recommend it to a first-time viewer who hadn't seen The Lion Guard before just because of how continuity driven it is. The whole thing has series-finale vibes and honestly I wouldn't be too surprised if the show ends with keeping the Guard out of the Pride Lands for good (giving them happy endings of course). Only thing keeping me from saying that is that I know Kovu and Kiara are set to appear again (per something one of the showrunners said on social media) and Nala's comment about being back in time for Kiara's first hunt; seems like a thread they wouldn't write her to bring up if it wasn't to set some sort of time point to loop back to in the last episode.
Scar is very clearly the standout character here given that we finally get to see the clearest idea of his backstory that we'll probably ever actually get. (And it's the best song of both the episode itself and the whole first batch of Season 3 stuff released so far.) Granted, it's a musical number montage of a single incident told by an unreliable narrator, but it's still something. I loved the expression on Scar's face as he watched Mufasa walk off; the telling of the story in isolation plus what happens to Kion later on paints the bite itself as the reason he turned bad, but you can tell just by the look that this was merely the final straw of a lifetime of resentment and Scar was always jealous and inclined towards vying for recognition through the throne. It's interesting to see how much of Scar's story has actually been told through Kion's experiences so far, but that's a bit I don't feel like writing out right now. Hopefully this isn't the last we'll get of him in terms of info and this sort of secondhand characterization.
Also, like aforementioned in a prior comment, holy crap, the show actually killed a character -- (in a pretty gruesome way too, and directly caused by one of the main characters nonetheless) -- and the one I really wasn't expecting at that. I actually didn't realize it happened until the next day when I was thinking about the show. Good on the writers; they planted the seed for that conflict throughout the series' run, right from the opening number in "Return of the Roar".
I also loved the consequences inflicted; for so long I've been wondering if the show would ever depict the guard not just losing a mission but actually suffering a potentially career/life-ending injury in the process, but I figured that'd be too heavy for a preschool show and they'd never do it. Obviously(?) things will resolve themselves but still, that moment in the lair of the guard was great, especially the bit where Ono loses his mark. It's so bittersweet and I love it; I wish more of the episodes had something like this.