It all depends upon how one is defining the spirit of fallout. The story of Fallout 3 follows an arc similar to the ones seen in other games, complete with the part where you inevitably fall upon the sword for the greater good (unless of course you actually play the DLC). The environment is well realized in general and seems to communicate a sense of desolate isolation common in the previous games. There was obviously a staggering change in basic gameplay and core mechanics, which is what I suspect causes most people who enjoyed the previous entrants in the series to complain. Rather than being an RPG in the truest sense, what you essentially get is a shooter with variable auto-aim and conversation trees. The options for problem solving at a player's disposal are limited at best as well, given your choice generaly revolves around which weapon you will apply to your problem of the moment. In past games, one could solve almost any problem without resorting to violence, and while I found this to be the most tedious way to play the game I did appreciate having the option.
In general, it is a game in the spirit of the predecessors but it does not slavisly follow in the tired footsteps of it's ancestors.