I liked Half-Life. Hell, I don't know anyone who didn't like Half-Life. I liked its first expansion, Opposing Force. It was a neat twist, and while you never actually played the bad guy per se, it did offer the series a closure that first game lacked (read: KA-BLOOSH!). However, it also unwittingly set a devious precedent - the story of the downfall of Black Mesa could go on forever, so long as you retold it from a different angle each time.
This worked for Opposing Force. For Blue Shift and Decay (the exclusive add-on for the PS2 port), the idea wears pretty thin. The stars are literally on the fringe of Half-Life's core narrative, which results in uninspired side stories about uninteresting characters.

The stories could have easily been tied together, but Valve didn't share any sequel notes they may have had with Gearbox, and they pretty obviously didn't give a rip about the events in Blue Shift. To Gearbox's credit, this game does fit seamlessly into the first Half-Life, giving Barney Calhoun a clear place in that timeline. But as far as being a story that needs to be told? Nuh-uh. He exists in the background, but he doesn’t do anything of significance. Barney Calhoun here barely meets Gordon in the course of the game, his actions have no impact on the events at Black Mesa, and his adventures here don't play into HL2 whatsoever.
So yes, it's disappointing. Saying in Half Life 2 that all along this Barney is the one that helped Gordon out (which he never does during Blue Shift) is completely pulling a George Lucas. I would think, at the very least, there could be a scripted event or two from Half-Life that you could trigger or have explained by Barney’s actions in Blue Shift. But nothing this clever ever happens.
Now that I've just kneecapped any interest you might have had, let's at least look at what Blue Shift does right.

When things finally fall apart, you'll probably feel a little underwhelmed. Aside from a very brief glimpse of chaos as the event unfolds (unique to this title) you'll take a concussion nap and wake up after things have mostly settled in. Aliens have entirely overrun the facility. The military is already in position. Gordon is nowhere to be found. This has the effect of dropping you right into the action, and sets up the game's policy of breezing through itself as quickly as possible. This a short game, and with all the pieces already in play, you're ready to cruise through the alien section, the military section, the Xen section, and the gizmo section in five hours or less.
Now, Half-Life, in my eyes, was more of an adventure than an action game. It did shooting well, it did suspense well, but it was at its best when you were stuck in precarious, rushed, life-or-death situations. Whether it was inching along a broken catwalk over a bottomless pit, or being stuck in a pipe with a satchel charge thrown in your face, these kind of Die Hard moments made the game for me. They're strangely absent from this title. Instead, Blue Shift focuses on the combat, which, while handled well, fails to make it anything special. You'll be facing the same run-and-gun battles as any other FPS, with the familiar Half-Life locales of sewers, offices, warehouses, train yards, and mechanical basements used as mere backdrops.
The most detailed sections simply act as arenas for large-scale battles - a couple of places in the train yard come immediately to mind, culminating in hosing down a stream of military grunts with a mounted machine gun. It's hard to classify as "boring," but without the vertigo-inducing environment sections, or the weight of Half-Life's story, it comes off like any of the good shoot-em-up fan maps you can download off the Net. For free, I might add.

Some have said that Blue Shift, clocking in at the five-hour range, is too short. Since nothing of consequence happens, and there's nothing new to play with, I would argue it's a perfect length. You get a sample of all the major points from HL1, a few new areas, and you're out before you really have time to complain. You won't even face a boss, or any complicated mechanical puzzles, just shooting interspersed with occasional bits of dialogue. The included "High Definition Pack" also offers a boost to textures and models that's impressive enough to install as an "eh, why not?" upgrade, but it's far from necessary. The Steam version omits this pack with its standard release, but you can download it as an update to all the original Half-Life games.
It's a nice length, some action happens, and limited ammo (plus the inability to recharge your armor) makes this one a slightly different challenge for Half-Life vets. If you want to play a small bit of Half-Life again, without actually playing Half-Life again, Blue Shift might be worth consideration. Just remember that the storyline here is as much of a throwaway as the generic guard characters it’s based off of, and none of the magic that made Half-Life a true experience is included. The Dreamcast asking price (a free addition) is exactly what it's worth.