
The exhaustion of food paves the way for Locke to emerge as the mysterious hunter, and so begins the first Locke-centric and an episode full of twists and turns.
The big reveal at the end is just one of the twists. We're led to believe that Locke is a very important man but flashbacks tell a different story. The first mention of Helen draws us into thinking she's a romantic interest, only to learn that "romantic" would be a euphemism in this case.
The island storyline is also full of memorable moments. Charlie and Hurley attempt to spear a fish (had me rolling the first time I saw it), Jack sits with Rose in a very touching scene, the Losties hold a ceremony by the flaming fuselage, and Locke brings Kate and Michael on a hunt for boar.
All these moments are weaved together very nicely without anything feeling forced. Minor deductions for the overly hostile Randy Nations, but otherwise excellent work here by David Fury.

It'd already been established that LOST was going to feature some excellent acting from an ensemble cast, but Terry O'Quinn absolutely set the bar in Walkabout. Right out of the gate he was asked to play the full range of emotions: bored and discouraged at his office job, shy and sheepish as he talked with Helen, reinvigorated and stoic as he hunted for boar, introspective at the end of the last scene. He knocked every single opportunity way out of the park.
Bonus points to L. Scott Caldwell and Matthew Fox for their shared scene on the beach. I just love that scene. Caldwell's delivery of "You have a nice way about you" just feels so genuine as does Fox's reaction.
Minor deductions for Harold Perrineau (normally a top-notch actor) for his scene asking Sun to "babysit" Walt. The gesturing and stuttering were overselling it a bit.

This episode didn't call for many special effects, and the ones that were used relied more heavily on the audience's imagination than anything else (i.e. trees bending and cracking while the Monster approached Locke).
From a directing standpoint, however, this was a strong episode. Locke's "condition" was effectively hidden until the reveal, and the sequence AFTER the reveal is a fan favorite. Hearing Giacchino's majestic music while Locke stares at his old wheelchair is cinematic brilliance.
Deductions for the boar sequences, which tried to sell realism with herky-jerky camera movements.

I'm in the minority here but I feel the Longevity bonus belongs to the island storyline more than the flashbacks. The fuselage ceremony and the Jack/Rose scenes never get old with me, and it goes without saying that Locke's condition can only jolt the viewer so many times. But this episode is so tightly woven that it holds up very well through repeated viewings.

I consider Walkabout to be the bellwether episode of the entire series. If you're new to LOST and the ending of this episode doesn't get you hooked, chances are you'll never find it to be your cup of tea.
I personally identify with Locke quite a bit, as I'm sure many others who've ever worked an office job can. Cubicle life has a tendency to make you want to pick up and go elsewhere, to feel important again — even if it's hunting boar with nothing more than a knife.