Somewhere in the moonlit Mojave wasteland a debonair post-apocalyptic gangster apologises as he takes careful aim at my head and explains to me that the game has been rigged all along.

Silly the things you think about in a moment like that. For myself, I’m wondering why I went to the effort of hollowing out perfect right angles in the shallow, dusty grave I’ve just dug for myself.

Am I stringing out my last fleeting moments of existence? Am I being obsessive-compulsive to the very bitter end? Has Dad’s lesson about “a job worth doing” finally sunk in?

Of course, it’s easier to ponder these existential details when you’ve lived through the same moment twice.

The scene is from the opening cinematic in Fallout: New Vegas and I’ve watched it twice over in quick succession because the review code I’ve been given is broken. Even before the game can reach its first auto-save checkpoint it has locked up on me. An Obsidian game, then.

A stand-alone addition to the franchise and built on the same bones as Bethesda’s Fallout 3, New Vegas goes west and moves the timeline forward to the cusp of re-civilisation. You play a courier who becomes entangled in a power struggle between several factions for dominance of the area.

Things get little better when minutes later you stumble from Doc Mitchell’s ranch into the radioactive glare of new Nevada. There’s no comparative sense of bewilderment, scale, excitement and fear that comes from leaving the oppression and claustrophobia of your vault for the first time – a secure underground environment where you’ve only heard rumours of clutching life above ground.

Instead, New Vegas drops you into post-apocalytpia roughshod.

Using the same engine as Fallout 3 means that the game also exhibits the same curiosities. New Vegas looks and behaves like it was built years ago. Non-player characters occasionally move and talk like marionettes; creatures sink into the ground and slide one another out of the way.

Then it locks up again.

But a poor first impression belies a larger experience that is in a great many ways richer and more immersive than the last instalment. New Vegas’ setting is more detailed and nuanced, its stories more compelling, its characters more convincing, its gameplay deeper, its humour blacker and its morality greyer. An Obsidian game, then.

And if for now you’re hitting the quicksave button with the same frequency as you’re hitting reload, it’s nothing a patch won’t fix. Publisher Bethesda has promised it’s already in the mail.

There’s no clear delineation of right and wrong or good and evil as there was in Fallout 3, only conclusions. As you progress through the game you’ll forge and break alliances with the wasteland’s factions, from the Romanesque Caesar’s Legion, an army of orderly if ruthless slavers led by a charismatic tyrant to the bureaucratic and perhaps too idealistic New Californian Republic.

The flagging Brotherhood of Steel seeks to exert new authority and control of the region’s technology and the powerful amoral criminal fraternities of the strip are sometimes the lesser evil.

If at first you can walk a tightrope between these factions, ultimately you’ll have to ally yourself with one and know that in doing so you’ve closed off vast swathes of content in any one play through.

Like the factions they belong to, the characters you encounter are rounded, engaging and sometimes duplicitous – none more so than Mr. House, a Howard Hughes-like recluse ruling over the Mojave wasteland and given voice by Murat Auberjonois.

But the game’s greatest strength is without a doubt its attention to detail. As you explore a map roughly equivalent in scale to that of the Capital Wasteland you’ll be rewarded with small touches. Each and every corrugated iron shanty tells a touching or humorous story about its former inhabitants.

Then you’ll pause to consider the effort that someone at Obsidian has made. Hidden away within those four rickety walls is an entirely incidental piece of background that the vast majority of players are unlikely to discover or care about, and yet, someone at the studio has obsessively decorated the enclosure so that the few who bother to go inside are rewarded.

At night the gaudy glow of the New Vegas strip always beckons over the horizon.

Obsidian has also buttressed the role-playing elements of Fallout 3. The available perks are vastly expanded and the melee weapons system has been overhauled to make it a much more attractive option.

Both of these are particularly important in hardcore mode, wherein ammunition has weight and where you’ll need to ensure that your character remains rested, hydrated and well-fed.

Hardcore is something of a misnomer, however. The mode doesn’t necessitate a more aggressive approach – additional hit points don’t fortify creatures and enemies. Instead, it’s a kind of enhanced realism mode. You’ll pause during your wanderings to consider sleeping on a soiled mattress, you’ll give serious consideration to the otherwise redundant “survivor” perks because you’re always lapping up any irradiated water you happen upon, whether it’s in a bottle or a toilet.

The only abrasive shortcoming in Obsidian’s embellishment of Fallout 3 that will not be fixed in the days or months ahead is the updated companion system. While you’re provided with an extended list of orders for greater control, in reality the AI simply isn’t up to scratch. Companions behave in a fashion that defies logic – no small feat for a system built on that very science – entering into battles with improbable odds, snagging on terrain and defying their orders.

Even so, Vegas represents a solid addition to Fallout canon. Those accustomed to investing hours examining endless story arcs, or searching vast environments for details will certainly appreciate Obsidian's efforts, even if newcomers may struggle to see what all the fuss is about.