The game is hurt by too many fantasy RPG cliches and poor implementation of some critical game elements.
THE GOOD: A fairly large post apocalyptic SW desert game world, which allows for sand box exploration, and features many real world locations of S California and Nevada; lots of above and below ground sites to discover; dozens of NPCs to meet and interact with via dialogue trees; multiple NPC factions to interact and develop relations with; multiple game paths and endings (depending on which faction/s you've aligned with). While the main game storyline is fairly short (not as short as many recent popular FPS games) there are literally dozens of side mission available (some remain unavailable depending on which NPC factions you're enemies with). You have the ability to pick the sex of your character and select a preset face or extensively customize it. At the game beginning you may customize your characters skills and abilities in many different ways, to allow for individually preferred game play styles. There are dozens of different ballistic, energy, melee and unarmed weapons to choose from to suit your individual game play style as well. Many traders to buy, sell, and trade "stuff" with, as well as purchase modifications for some of your weapons. The Developers have made a modding tool available; so gamers may mod many different aspects of the game they think could be better or different than the vanilla game experience. There are a ton of mods available online from numerous sources; that address aspects of the vanilla game you may not care for.
THE INDIFFERENT: FNVs graphics are DX 9 based and look rather dated this late in 2010. The games overall GFX look remind me of STALKER: SHOC from 2007. Game sound is OK as well. There are five different difficulty settings available; though it appears their only in game affect is how much damage your and enemy weapons do to each other. Besides the difficulty settings, there is a hardcore mode available which makes it necessary for you to monitor and care for your characters in game food, water, and sleep needs. While on the surface, this would seem to add to "immersion" it's implemented in such a soft fashion it's basically meaningless and tedious, rather than immersive. Your character has significant ability to create a variety of objects, potions, and devices in game (depending on your characters skills and abilities), as well as perform weapon and clothing/gear repairs. The day/night cycle in the game is superfluous as nights are so bright you can see very well anyway. There are a number of NPCs you'll encounter who can become companions for you, on your adventures, you may engage in additional dialogue with, and will give you at least one side mission of their own, as well as provide you with a "perk" unique to each character. The combat system is fairly normal, though the much touted VATS system, allowing you to target specific body parts of enemies before firing/using your weapons is over rated, not very effective in many encounters (allowing other enemy NPCs to beat the snot out of you while you're hung up in slo mo VATS ballet), and provides a constant break in immersion.
THE BAD: An overbearing omnipresent inventory and information management system that constantly breaks immersion (I find myself spending 20 out of 60 minutes putzing around in my "Pip Boy 3000). The weapons suffer from the curse of game developer "balancing", so you have pistols that are more powerful than assault rifles, and unarmed weapons that are more powerful than either pistols or ARs.
Weapons that have real life counterparts or analogues are very underpowered compared to them. That under powering is necessary to compensate for the terrible enemy AI, who once they become aware of you will invariably run at you in a straight line (depending on the terrain between you and them). The effectiveness of weapons are arbitrarily affected by your RPG skills and abilities (not by your actual gamer skills and abilities). The game is cursed with RPG clichés like skills and abilities that substitute for Fantasy based RPGs enchantments and spell casting, these break immersion and have no real place in a Sci Fi based RPG. Experience points and leveling up are additional RPG clichés that arbitrarily affect your characters ability to accomplish in game tasks, or solve puzzles regardless of whether you (the gamer) know how to, and have the ability to solve the task or puzzle. At times non sensible dialogue trees (e.g. you've just spotted enemy units on patrol nearby but the dialogue tree with friendly NPCs presents no option to tell them about it as you would in real life). Your character never speaks in dialogue; you click on you conversation choice from the menu and the NPC you're interacting with speaks their next line; this was bad in the Half Life series and is here too. Frequently plot lines and actions which are supposedly dependent on plot developments external to your characters actions are actually totally keyed to your character and their position in game e.g. while siding with the NCR in the climatic Hoover Dam Battle, the Romans aren't attacking the Dam, as the story line says; they're attacking my character. If I hold position and don't advance no more enemy appear; if I advance past a trigger point the next group of enemy invades the map, makes no effort to attack and occupy the dam, but spend all their efforts attacking my character. That is poor story writing, or implementation, and badly breaks immersion.