BioShock will inevitably draw comparisons to other FPS and RPG hybrids.
When Half Life, System Shock 2, Thief and Deus Ex came out, those games offered variations to the basic premise of the Doom FPS gaming experience...those games each took the basic gameplay elements of a FPS and introduced something that initial Doom clones lacked...a compelling or engaging storyline, an interesting world to explore, and alternatives to run and gun gameplay.
Sure, each of those games had their flaws, but given the technology at the time, they were all outstanding games. It is difficult to replicate the experience of enjoying those game playing environments for the first time, because at the time it was something new and fresh.
Look at Half Life 2...essentially an updated version of Half Life...all of the gameplay elements that made Half Life a classic were present in Half Life 2, but with a shiny new interface and other interesting gameplay elements. I didn't find HL2 as enjoyable as the original, but that didn't make HL2 any less of a great game...and the story of Half Life is what drove me forward long after I got bored with the gameplay, because I want to know what happens to Gordon Freeman and how is story will play out.
Is BioShock a revolutionary step forward in FPS gameplay...perhaps not...but it is definitely evolutionary in that it incorporates some of the best gameplay elements of a FPS, and packages them into a very interesting environment.
Arguably, what makes BioShock great is not the gameplay but rather the city of Rapture itself...I never bothered with FEAR because the premise of the game didn't interest me...yet another run and gun FPS through an urban environment, but with a supernatural twist.
Rapture, and all of the sick and twisted things you encounter along the way, is what makes BioShock unique...when I kill a Splicer or Big Daddy, I actually stop to examine the corpse because of the amazing art design that went into those characters...I have never done that in a FPS before...when I encounter a new area in BioShock, and clear the area of threats, I like to walk around and just examine all the attention to detail in the level design...never bothered to do that with another FPS either.
What I also like about BioShock is that the progression is slow...there isn't a sense of urgency to rush through one level to the next...I sometimes go back to previously visited areas just to test different plasmid combos on the weaker and earlier Splicers.
Is BioShock the greatest FPS of all time...of course not...but it should make the top ten IMO...but here are my favorites of all time:
Doom (only because it started it all)
Half Life/Half Life 2
Dark Forces/Jedi Knight series
System Shock 2
Deus Ex
Thief series
BioShock
FarCry
Tron 2.0
Quake 2
Call of Duty
No One Lives Forever
Clive Barker's Undying