Nutshell: Not bad. An interesting theme about the Federation and some good backstory of Tuvok. Unfortunately, the ending doesn't amount to much; the show really could've been much more.
Premises like "Flashback" are what make the Star Trek universe so immortal and endearing. If there is one reassuring thing about the way Star Trek sees itself, it's that it knows what it is and where it came from—and "Flashback" remarks on this. At the same time, "Flashback" is a decent story. Not great, mind you—sometimes the events of the story can barely live up to the impetuses behind them—but it's definitely passable and worth the effort.
While searching for energy sources, the Voyager ventures near a nebula. The nebula's visual appearance triggers the surfacing of a repressed traumatic memory in Tuvok's subconscious. Due to convoluted Vulcan mind workings explanations, the Doctor says the memory must be brought into Tuvok's conscious mind and reconciled, otherwise Tuvok's brain will be irrevocably damaged by the side effects. Tuvok must mind meld with Janeway (his closest personal tie on the ship) so they can search through his memories for the repressed culprit. In the process of the mind meld, however, Tuvok and Janeway somehow end up reliving Tuvok's first Starfleet mission aboard the USS Excelsior under Captain Hikaru Sulu (George Takei), some 80 years ago.
Does this sound like a Brannon Braga concept? Braga always seems to enjoy toying with mental states, reality, time, and the like. While Braga's script for "Flashback" is nowhere near as labyrinthine and interesting as his "Projections" was last year, "Flashback" does have its moments of character inspiration and inevitable nostalgia.
Part of the fun of the episode is how it bases its story on "actual" past Star Trek events (that is, Star Trek VI: The Undiscovered Country from the Excelsior's point of view). For example, remember the cup of tea Sulu was drinking in the opening scene of Star Trek VI? Well, I took great enjoyment in finding out it was a Vulcan blend that a 29-year-old Ensign Tuvok gave him—perhaps "trying to make Lieutenant in a month" Commander Rand (Grace Lee Whitney) observes.
Ah, I suppose only a true fan of the franchise could find such fun in such a simple little detail. But for that matter, I also found the recreation of the Praxis explosion shock wave scene from Trek VI to be interesting (if, for no other reason, because of the technical and directing implications).
I also appreciated Braga's attempt to show Sulu in action. For the attempted Trek VI rescue of Kirk and Bones from Kronos, Sulu takes the Excelsior through a nebula to avoid a confrontation while illegally venturing through Klingon space. The evasive techniques are not completely successful, however, and Sulu runs into a Klingon ship commanded by Kang (yes, everybody is popping up here), which leads Sulu to claim he wandered in and got "lost"—a claim he can't even keep a straight face through.
Superficialities aside, the real reason this works is because it makes some statements about both Tuvok and the Federation in the process. When Sulu announces his intentions to violate Starfleet Command's orders and venture through Klingon space, Tuvok speaks up—he points out that it is a willful violation of regulations, and that he must formally protest his captain. "A pretty bold statement for an ensign with only two months space duty under his belt," Sulu remarks, not happily. Sulu's subsequent comments about how duty and loyalty to fellow officers sometimes warrants bending or even breaking the rules makes a lot of sense, and seems credible given what we know of the character.
This further confounds Tuvok, who, fresh out of the Academy, has not had pleasant experiences with human behavior. As Tuvok and Janeway probe through the memories, the flashbacks take us to a scene after Tuvok's confrontation with Sulu, when a discussion between Tuvok and his bunkmate Valtane (Jeremy Roberts) reveals a Tuvok who did not particularly like the presumptions of humanity. "You believe that everyone in the galaxy should be like you, that we should all share your sense of humor and your human values," Tuvok tells Valtane. Russ' performance is good, as usual, creating a young Tuvok who was not pleased with human arrogance and narcissism—in fact, if we didn't know Vulcans better, we might sense some actual anger here. Tuvok's subsequent discussion with Janeway on the topic is one of those Quiet Dialog Scenes, but one of the better Quiet Dialog Scenes on Voyager's record—it was nicely performed and directed, and there was some genuine impact and character backstory development here. By the time the scene was over, I felt like I understood much more about Tuvok than when the scene began.
The other thing "Flashback" gets right is its observation of differences between time periods. After an unsuccessful meld, Janeway goes to her ready room to study up on the Excelsior—only to discover the mission she's looking for was never logged because of its illegality. Kim is astonished—a Federation captain falsifying his logs? It was a different time for Starfleet, Janeway explains, and Sulu belonged to a different breed of Starfleet officers. "They were a little slower to invoke the Prime Directive and a little quicker to pull their phasers." This is a good point, and it's well said. It's nice to see the newest of Treks acknowledge is heritage, and it's intriguing to note the differences between the 23rd and 24th centuries. It shows that in 80 years there has been significant progress in the Federation, and that people do notice such progress. Nice work.
But what does all of this have to do with the repressed memory? Actually, not a whole lot. One big problem with "Flashback" is how the repressed memory figures into the equation. The main goal for Janeway and Tuvok is to hunt down this memory, but they can't figure out why they keep ending up in Tuvok's memories of the Excelsior. In a plot move that is all-too-typical, the repressed memory turns out to be a parasitic sort of "virus" that hides itself from the immune system by disguising itself as a traumatic memory. Apparently Tuvok has been carrying this virus since Valtane's death on the Excelsior, when it "migrated" hosts—that is, from Valtane to Tuvok. (No, I won't delve into the inevitable implausibilities of this idea.) The ending, in which Doc and Kes kill the virus by irradiating it, is a somewhat effective mishmash of jarring visuals and sickbay technobabble (and a decent score by David Bell), but it has no lasting emotional impact. If the repressed memory had actually been a real repressed memory with some sort of character significance instead of a quasi-red herring, the show could have had much more lasting impact.
Oh well. I'm inclined to ignore the entire repressed memory portion of the show. It's little more than an excuse to launch the flashbacks of Tuvok on the Excelsior, anyway. Fortunately, between the character backstory, the comments on change, and nostalgia for the 30th anniversary of Trek, the ends justify the means.