how much of the game will be lost forever? i don't normally play games this open-ended, so I assume it'll be a few dozen hours before my character is strong enough to do whatever to whomever. if i just run around acting like an ass will it ruin the story aspect of the game, or will people respawn?
For that matter, how long does it take before I'm an ass kicking machine, on average? I just want to get into badass gunfights and I don't really want to work for it.
there are a lot of random people you can just kill without it affecting the story directly other than your reputation with the faction, but as a rule if they have an actual name killing them may cause a quest to fail which can affect the story.
unless you cheat horribly you will still lose fights vs most major characters anyway, until about lvl 15ish depending on the gear / skills you take (A decent stealth build with Chance's knife can kill lots of things from behind that he probably shouldnt be able to)
of course this is an RPG so the idea isnt to kill everyone anyway, you will miss a large chunk of story and missions if you just kill people as soon as you meet them :P
^Agree with above. Unless you are just doing a speed run to the end and don't want side quests, hold off until you have a better idea of who they are. Even when you are told to take out someone for one character/faction, especially a named char like the above poster said, you can still affect other quests.
Ever so slight spoiler example:
Someone in the NCR wants you to deal with someone in Vault 3 and you kill them and think it's all fine. Then you are screwed for carrying out another set of quests with the Khans and it becomes difficult to deal with some of them and you have to do a lot more work to get around the problem you created from being quick on the trigger. Lots of unexpected connections in the game.
So if you want maximum value from the game, hold off killing anyone but random generated enemies. Keep in mind that since there usually isn't an immediate time limit to do quests, there's always time to kill people after you've fully exploited them and milked their quest lines.
Besides, since there are usually random generated chars all over the place, it's not like you can always have the satisfaction of making most areas completely lifeless. --- I, for one, welcome our new feral ghoul overlords! (call me pv -it's easier)