My least favourite FO3 expansion is ironically the one I enjoy talking about the most because it's uniquely terrible.

On the surface it's (ostensibly - I may be putting too much faith in the writers) a straightforward parody of what was, at the time, every shooter on the market: You are simultaneously a nobody and a legend, the entire US military cannot do anything without you, and there's no real way to engage with the world beyond murdering people in linear, grey hallways.
This is only aided by the in-universe notes/audio logs that make it obvious the simulation is massively detached from reality at the behest of an insane, sinophobic American general. So it's an in-universe parody as well an out-of-universe one.

There's just one big stinky winky dinky problem:

The parody doesn't work because the core of it is what Fallout 3 already is.

Fallout 3 at its core is a game where you walk through unwieldy shooting galleries in boring environments, endlessly massacring nearly everything you come across in areas that're 99% of the time either linear hallways or intersections that lead to linear hallways.
The only meaningful difference between OA and the game it's bolted onto is that Fallout 3 very occasionally pretends to be an RPG and lets you talk to someone. Even then, 9/10 times you either kill them or having a big prompt that lets you do so.

Perhaps what makes OA so much worse is that it's a thinly-veiled excuse to deposit some loot on you. Your incentive to do the DLC isn't "see this cool place", "free some slaves", "finish the main story" or "aliens, right?", no. You're told in no unclear terms that you should do this DLC for the loot that's in the vault. That's it.

I'll speak on it in more depth when I finish the actual Fallout 3 review, but the actual rewards you get really compound the game's overall issue with loot being meaningless. Namely, OA is perhaps the only part of FO3 that features a reward dump that isn't shit. The stealth armor, winterized T-51B, shocksword and gauss rifle are all excellent regardless of one's build, and given how easy OA is they're functionally free.
But there's a lot in the vault that I can only describe as nothing more than shelf-filling garbage. Upon slogging through OA and opening it, you'll be met with uh... A Chinese Assault Rifle, some ammo for it, and a Missile Launcher, alongside lots of mines and grenades. All incredibly common loot in the wasteland, to the point where I don't blame anyone for thinking the vault is bugged when they see so much trash loot.

And, all things considered, it probably is bugged or at least unfinished. As is the norm for Bethesda games, there's a bevy of cut content for this DLC and the vast majority of it is stuff that'd fit in the loot vault - most noticeably reskins of the sim weapons but without the bloated HP. Which would still be unremarkable, but at least it'd be unique - that simulation exclusive Chinese Assault Rifle looks gorgeous.

The extra 0.5 of a star rating only comes from me having played this through Tale of Two Wastelands, which makes it less of a slog (due to your armor's DT/DR outclassing that of your enemies) and fills the vault with all the aforementioned cut content - plus some other goodies.

The only saving grace to this DLC is that it's perhaps the first and only time I've agreed with people who're fans of Bethesda's Fallout: They hated it at release, so do I.

They still hate it in 2024, and so do I.