Most games today aren't fun because game companies make them in a simplified manner to appeal to the masses of casual players and make a lot of profit. The fact that you noticed they aren't fun makes you one of the minority of surviving hardcore gamers like me. My advice is to return to replaying real manly games that you'll find out they're actually fun to play again, even though you have played them until they got boring before. There are actually still games like that coming out lately, but only 1 or 2 per year, and they are usually indie games so they don't get very famous.
Here's my recommendations on great first person shooters that never get old and will be always fun to play. Best FPS games of all time (in no specific order) are:
The Ultimate Doom, Doom II: Hell on Earth, Final Doom: TNT Evilution, Final Doom: The Plutionia Experiment
Quake, Quake: Scourge of Armagon, Quake: Dissolution of Eternity, Quake II, Quake II: The Reckoning, Quake II: Ground Zero, Quake 4
Unreal, Unreal: Return to Na Pali, Unreal 2: The Awakening
Serious Sam: The First Encounter, Serious Sam: The Second Encounter, Serious Sam 3: BFE
Half-Life, Half-Life: Opposing Force, Half-Life: Blue Shift, Half-Life 2, Half-Life 2: Episode One, Half-Life 2: Episode 2, Portal, Portal 2
Descent, Descent 2, Descent 3, and their expansions (can't remember the names)
System Shock, System Shock 2
Duke Nukem 3D: Atomic Edition
Alien versus Predator, Alien versus Predator 2, Aliens versus Predator 2: Primal Hunt
Great FPS games, that cannot be called the best but are still good enough to be played again and again are:
Doom 3, Doom 3: Ressurection of Evil
Prey
Pariah
Serious Sam 2
Will Rock
Painkiller, Painkiller: Battle out of Hell, maybe the newer titles too but I haven't played them yet
Turok: Dinosaur Hunter, Turok 2: Seeds of Evil, Turok: Evolution
Command & Conquer: Renegade
Clive Barker's Undying
Return to castle Wolfenstein
F.E.A.R., F.E.A.R.: Extraction Point, F.E.A.R.: Perseus Mandate, F.E.A.R.2: Project Origin
Great tactical FPS games, if you enjoy them. For me they are not games that I can play every day, but when I get in the mood they are fine games too.
Delta Force, Delta Force 2, Delta Force: Land Warior, Delta Force: Task Force Dagger, Delta Force: Black Hawk Down, Delta Force: Team Sabre
Project I.G.I., I.G.I.2: Covert Strike
Far Cry, Crysis, Crysis: Warhead
S.T.A.L.K.E.R.: Shadow of Chernobyl, S.T.A.L.K.E.R.: Clear Sky, S.T.A.L.K.E.R.: Call of Pripyat
Operation Flashpoint: Cold War Crisis, ArmA: Armed Assault, ArmA 2, ArmA 2: Operation Arrowhead, upcoming ArmA 3
Quality multiplayer FPS games, not listed above:
Quakelive
Unreal Tournament, Unreal Tournament 2003, Unreal Tournament 2004
(Half-Life: ) Counter-Strike
Battlefield 1942, Battlefield 1942: Road to Rome, Battlefield 1942: Secret Weapons of WWII, Battlefield: Vietnam, Battlefield 2, Battlefield 3
There are others, but I can't remember them right now. But pretty much all FPS games that came out during the period of 1993-2003 deserve to be tried at least once. So there you have it, if you haven't tried any of these, do so, and if you have played them but not recently, play them again!
Turning a blind eye to the console crap that's being sold today and playing what we know is good even if it's old is the only thing we can do in these dark times