Minigun Jim
It Wandered In From the Wastes
If you want you mod to blend in with the original, then using the same design cues and detail level is important. Unless you upgrade all the graphics, then the odd high-res item will stick out like a sore thumb.Some of the weapons are more modern, but there are far more other items than those in his art pack. But, overall, your argument makes no sense, unless you are choosing to equate 'Fallouty' with 'less detail'.
The Fallout universe is basically 1950s/60s retro-futuristic, i.e. what designers and scifi artists from that era figured the future was going to look like. Basically "what we have now but bigger and faster". They never saw microchips coming for example, hence the big use of vacuum tubes in FO2 designs. dd to that the fact that almost all the item images from Fallout 2 have a "chipped and dented" or "well used" feel to them somwhere from decades of use in the wasteland, and straight rips of modern pictures start to jar with the style. A good comparison is the shovel with the brand new label as opposed to the usual beaten-up model, or the DDR RAM memory modules as opposed to the wire and vacuum-tube filled originals.
The items are very well 'shopped, but the source material doesn't fit in with the Fallout theme. Now if anyone planned a "21st Century Sci-fi" total conversion, these would fit right in, along with an iPhone-esque Pipboy and a Land Rover as the car. That's not sarcasm by the way, an updated era would be an interesting but probably impossibly time-consuming mod. My preference would be the 80s though, with more of a "Terminator" or "Alien" future feel.
However to make it integrate in the original style of the game, better source material would be stuff like shots of vintage stuff on eBay, pictures from stuff like old Popular Mechanics magazines (see here for archived)
Or for the modern weapons, take some shots and duff them up a bit in Photoshop. Add on a bit of dirt, scratches, cruder wooden handgrip replacements and the like. Make it look like it's keeping going in the face of a century of harsh use or storage in a dusty abandoned base.