Will the game bore me? Can I roleplay? Are the weapons and story good? Anything I should know?
Turn based vs realtime? Cats vs dogs. Beer vs wine. ect. Both work for me.
Isometric view vs 1st person? Same as above. Personally I prefer isometric person view in RPG's, old habbit.
Old vs new?
In computer games tech and game design have often improved. Still old classics often have better story even while visual effects aren't as neat as in newest blockbusters. New computer games are much more expensive to make: Things taken as granted in newer games like voice actors, do cost production money. Better screen resolutions increase need for graphic desingers, while better modelling tools also make their job easier. When two original Fallouts were made games were often done with smaller budgets and design teams, Black Isle due to that had bit more creative liberty in case of potentially morally offensive issues. six, drugs, gambling... etc. Annoying kids can be shot or killed in other ways and you don't have save those brats. Companions can be sold to slavers. Lot more filth and brutality. Difference is like between 50's westerns and spaghetti westerns or Shield and 60's police shows.
Stories, humor and game mechanics?
There is more opportunities to play bad character and lot more choices to make in game. Quests in both I and II have more alternative ways of doing and more alternate endings. In general combats can be avoided in most cases and most quests have other ways to solve than shooting the bad quys. They often offer bribes to kill guy hired you to kill them or you even can choose 3rd option: kill both original employer and guy who tried to bribe you and keep all their money and stuff. Due to more optional ways of doing things there are lot more working character builds. Basically only "must have high" stat is INT, even then there is option of playing INT 1 or 2 character who is too stupid to speak. CHR is lot more useful than it is in third game. So are PER and AGL as they affect combat lot more due to turn based system. Characters also have option to take traits that are like perks but also include bad things, traits affect characters a lot. Gain some and lose some.
Original Fallouts have lots of popular culture references and jokes. Most of those are also bit nastier, like certain grave yard scene witch might resemble The Good, The Bad and The Ugly.
Fallout 3's story is more character driven than original games stories are. I think first has best story. Second part has probably best quests and part of story, but as whole story isn't as good as first. In case of playing in alternative ways second game has most options and it's probably most versatile single player RPG ever published.
With both first and second parts fan made unofficial patches are something that I do recommend as must do thing. Killaps Fallout 2 restoration project-mod improves game a lot by unlocking huge number of game features that didn't work in official publication due to bugs and adding content that was planned by makers but they didn't have time to make properly.
Weapons?
Gauss pistol+fast shot+bonus rate of fire+better criticals+action boy (x2)+bonus ranged damage(x2)+sniper+Luck 10+couple shots of Jet=Do you really think that gatling laser packs punch?
Buy 1&2 and stick with them for a while, it might take a few hours for you to get past the turn based combat and the sparse graphics but once suspension of disbelief kicks in you should find yourself in one of the most well realised rpg worlds ever created.
They're so cheap you owe it to yourself to give them a try
I personally recommend to buy collection that also has tactics. Retail price is about 20? or $, older game collections and reprints are often in discount. I paid 9.99? for collection couple years ago as I had lost disk of first game.