ok wildly OT post time:
its not like the black isle games, imo the immersion is better due to the perspective and extra detail however playing the games without mods is like any bethesda game post daggerfall without mods "average", however moding the shit out of it, makes the game alot more fun and plays more like deus ex with a pause for aimed shots
looky here for my mod post
http://www.neogaf.com/forum/showpost.php?p=15258670&postcount=10315
basically in un modded fallout 3 you got way too much xp, vats was way overpowered (you took like 10% damage or something) and you could basically swim in radiatited water no problem, with the mods I listed you will die fricken fast fighting mutiple peoples if you dont use cover/mines/targeted shots to disable them, water is certain death without a load of rad-x and radaway, and you need to eat, drink, and sleep. Also limb damages hurts you badly (in movement speed, accuracy, or perception) and same now goes for enemies.
if you get fallout 3 get the pc version and imo play it once unmodded (you will pwn everything) then again with the mods i listed. I loved the turnbased fallouts (had them when they were new) but with mods fallout 3 plays like an rpg-lite strat based fps.
The writing however isnt near as good as black isle, but the world imo is better if only for exploring and coming across cool stuff.
Unmodded Fallout 3 as a fallout game: C-
Fallout 3 as a PC RPG - C+
Modded up fallout 3 B+ imo ( it still wont be turned based, but itll be more balanced, deadly, and unforgiving, which is imo how it should be)