OK, so here are my overall impressions of Fallout so far (I'm at Necropolis now, got bored so I'm taking a break):
1. Setting - Good
I appreciate the "purity" of the setting in Fallout. So far aside from Loxley with his British accent, most things have felt totally in place. However it also suffers from a lack of being fleshed out. You don't see communities struggling with starvation, or lack of water, and rarely do you even see individuals struggling against each other or against environmental forces. Everything feels too settled and stable, and very often the gameworld actually feels boring.
2. Intrigue - Very Poor
Unfortunately, there is no discovery factor so far. There is nothing to unravel, almost everything is at face value. Unlike in Fallout 2 where you could unwrap the tangled relationships between different towns and factions (for example, the families in Reno were allied with various external forces such as the Salvatores and the Enclave, the power struggle over Broken Hills, etc). There just seems to be very little to nothing going on "behind the scenes" in Fallout.
3. Content - Utterly Pathetic
Most areas are completely empty and have nothing to do. Shady Sands west has only the two central quests and no one to interact with except 4 NPCs all related to those quests. Shady Sands east is empty and useless. Junktown has 3 areas with 3 quests distributed across these areas. Necropolis area one has nothing to do except kill feral ghouls, and underground you waste time on 3 molerats. Vault 15 has nothing to do as well except kill rats, etc. The most content rich town is so far the Hub but that is only comparable to the Den, and quests are mostly localized. Perhaps 95% of all NPCs in the game are civilians and guards with only floating text, and out of the rest 2 out of 3 NPCs are useless to talk to and ignorable during a replay.
4. Reactivity - Poor
This is in relation to content. If a game has as few quests as Fallout, the gameworld could at least react to those quests. It's a shame for example that in Junktown no one even recognizes that Gizmo has been disposed off given that was the main quest in the town. Even after siding with Killian, he resets to his default dialogue as if you were a stranger that just wandered into the shop. Basic options such as being able to report Doc Morbid, or reporting the iguana guy are not even available. I can forgive lack of reactivity in a content rich game, but in a content poor game, these become much more glaring flaws.
5. Connectivity - Very Poor
It's funny how fans claim that the towns in Fallout 2 exist in isolation, whereas in fact most towns in Fallout 1 really don't interconnect at all. The only "glue" actually turning this whole thing into a setting instead of a random pastiche of small and uninteresting settlements is the Hub with the caravans going out to other towns.
6. Dialogue - Very Poor to Functional, with a few high points.
There's rarely any flow to dialogue, it often ends randomly like the designers couldn't be bothered to link various dialogue nodes, much of it is amateurish, some of it terribad (like in the Khans). Usually the best it approaches is functional, with the high points basically being some of the Vault Dweller's smartass comments and a few key characters (the jokes about Gizmo, for example and most of the Hub's major characters are generally well written).
7. "More than the sum of it's parts" factor - Good
All that being said, this game does have it's charm, it's fucking Fallout afterall. And for some reason despite being severely flawed is still overall a good game - weirdly enough, and I can't explain it myself.
ADDENDUM:
I can see how this game could be a lot better during a replay, simply because it is very possible to basically blind yourself to all it's flaws, which is probably why it has so many fans. If you already know that no one will react to Gizmo being killed, you won't bother talking to them anymore. If you know that 3/4 characters will have shitty dialogue and are of no consequence, you can simply ignore them, if you know an area is actually empty you won't bother exploring anything, you won't waste time looking into containers most of which turn up empty, or looking for quests where there are none to be found. But as a first timer, particularly one already used to Fallout 2, Arcanum and other games, it's a really disappointing and overall crappy experience finding mostly empty towns, characters, containers, etc. Basically, I now understand what it's like to play Baldur's Gate 2 and PST first and then move on to BG1 afterwards.