One aspect I agree with Zetetic on is that the minor locations in F3 always seemed packed with little things that fleshed out the Capital Wasteland, "story loot" if you like - diary fragments, downloadable computer files, Pip-Boy logs, that sort of thing. You'd find the skeletal remains of a couple lying on an old four-poster bed in some shack or abandoned building, two blood stains on the wall, a teddy bear on the bedside dresser, and a pistol minus two shots from the clip next to them. Looking around you'd discover the last few pages of the man's diary and read up on their suicide pact...wonderful stuff. None of this had any bearing on the story of course, but it was very cool to just happen across these little human tragedies that gave life to the gameworld. This sort of thing did appear in New Vegas, but not nearly as often unfortunately. I could have done with more of the likes of [spoiler]Trash, the death-obsessed goth chick who wants to become a ghoul but ends up carking it from radiation at the old A-bomb test site[/spoiler].
I mentioned the Wanderers Edition a few pages back, and it is absolutely essential for anyone playing F3. I actually liked the guns - never enough of them, man! The 19th & 20th Century Weapons mod is another classic. Only thing that one got wrong was the Lee-Enfield, which became the beast it really is after I modded it in the GECK to reflect its insane real-life firing rate. Now that the Gun Runner's Arsenal is out (only about a quid, buy it), plus all the other fan-mad mods, I think Vegas trumps it though...a fully-modded semi-auto 25mm grenade launcher is truly a thing to behold. The switchable ammo system adds so much to combat gameplay, and I never go anywhere without a full load-out of high-explosive, plasma, pulse, and stun 25mm to 'nade the shit out of anyone from 100 yards plus +. A modded Riot Shotgun or SPAS-12 (Reload mod) with flechette ammo is a fucking beast too. Haven't tried Project Nevada yet, but I will since I just finished my first Caesar's Legion playthrough last night at level 50, after more than 170 hours of gameplay, and am now building a low intelligence, high strength/endurance, NCR-lovin' melee n' fisticuffs moron for the next run.
Given the quality of writing for Caesar as a character, it's a real shame that the Legion quest path is so short and unsatisfying. As I've mentioned before, one of the things that worked really well was the way the soft-headed idealism of the Followers of the Apocalypse has unintended and often terrible ramifications...[spoiler]Caesar himself is a former Follower, his knowledge of history and martial arts training helping him put together a revivalist Roman army and cult of personality[/spoiler]. The Great Khans use their medical know-how gained from the Followers to make and flood the wasteland with drugs, in turn supplying the Fiends who cause chem-induced havoc. All great stuff, but I wish they'd expanded on Caesar's relationship with the Followers a bit more. It's all sort of glossed over as it is.
Despite the universally awful companion combat AI, Veronica was so much fun to travel with. Well written, appealing, funny, and Felicia Day was a shrewd choice on the part of the devs. Moreover, it was great to finally see a gay/lesbian game character who wasn't defined solely by their sexual orientation for once. I'd say the same for Arcade Gannon. Boone was an asswipe, but similarly well-realised, and his quest is one of the more satisfying in the game. The companion quest for Cass was probably the best, requiring you to make potentially serious, game-altering decisions. Her backstory, with its nods to Fallout 2, managed to connect the two games in spirit without overpowering us with the sentimental reek of fan service. Not a good character to travel with if you're playing an Evil courier, so I really didn't have any choice other than see her emulsified by the Van Graffs. ED-E really came together as a character during the surprisingly good Lonesome Road. I haven't taken Raul or Lily out on the road yet, but will do in my new game.
Apart from the huge, near inexhaustible number of potential quest/character choices, the thriving and often hugely talented modding community is what really makes these games so replayable. Yes, there is the usual "make your character look like a blue-haired post-nuclear anime character" from the Jap-loving perverts, and the obligatory breast mods aimed at 15yr old sad acts, but plugging a .50 calibre semi-auto Barrett sniper rifle with armour-piercing-incendiary ammo into a dull savegame is going to enhance any playthrough (I see that Project Nevada gives you an FN FAL, so I am ON that shit right now). Josh Sawyer is a well-known gun nut and I think the fact is well reflected in New Vegas.
The aforementioned Reload mod really sorts ammo crafting out, bringing it up to real-world levels of accuracy and detail (load up with dozens of different bullet types, hollowpoint, softpoint, semi-jacketed, armour piercing, cast lead, incendiary, full metal jacket, jacketed softpoint, lead round-nose, lead flat point, etc. etc.). Armour-piercing ammo works both ways though, so be careful. Weapon Mod Expansion gives you about 100 new mod options, and the ability to trick out the unique weapons (stick a rapid-fire firmware module on the 40mm "Mercy" grenade machine-gun, for example). Tailor Maid lets you play dress up with dozens, hundreds maybe, of armoured shoulder pads, pauldrons, shin guards, boots, gloves, scarves, hats, backpacks, ammo belts, bandoliers, etc. so with a little customisation you can run around looking like a member of Immortal getting ready for a photoshoot reunion.
Quest modding is the only area where pickings are thin on the ground, for obvious reasons, but I recommend New Vegas Bounties 2 without hesitation. The original was great fun, but this manages to top it in almost every respect. For an amateur production the voice acting is pretty good too, and you are well rewarded with a mix of caps, loot, and unique weapons. A highly entertaining way of filling time between main quest missions, you really need to get this - simple as that.