The twists and turns of this episode were fantastic, and made for a great departure from the classic SVU formula. The ending, however, left me feeling a bit empty-handed. The script just had too many characters, I think, and it was impossible to develop them all properly within 45 minutes. We didn't really get to know the villain(s) or truly understand their motivation. Too many people with hidden motives and not enough time to explore them all.
The strong point of this episode was Luna's turbulent character arc, brought to life with a gut-punch by Radha Mitchell's phenomenal performance. She's a wealthy, intelligent, attractive woman, the CEO of a fast-growing business whose purported mission is to empower women. But the strengths that have led her to success may also be her deepest character flaws. This eventually triggers a chain of events (spurred by other nefarious forces) that culminates in an archetypal descent into madness.
(To its credit, the script doesn't explicitly pathologize her behavior, but I'm unofficially diagnosing her with Histrionic Personality Disorder.)
Overall, despite a poorly fleshed-out conclusion, the episode stands out in Season 21 for its unique plot line and great guest actors. If you only watch a handful of episodes from this season, "Swimming with the Sharks" should be one of them.