Absolute crock of....
Valve hasn't followed on its successes???????
No Valve moved on and did something different instead of vomiting the same junk on people. Portal & Portal 2, Left 4 Dead and Left 4 Dead 2. Team fortress etc etc.
Halo just continually pumped the same crud out in sequel after sequel adding little more than a few weapons or a new vehicle or a new location to what was the same engine. Plot moved on a bit but not much and if you play the ODST it isn't even much of a plot jump.
Even your own review just says Halo 4 is a clone of the first Halo with nicer whistle & bells.
What actually happened is a good formula from the likes of any PC game before it like Half life, was put onto a console where a captive audience of people who have no attention span and where logic and brains are not required can run round shooting everything in a linear fashion. Run jump shoot, hide, run jump shoot. (can you even crouch) Then on every incarnation since it has repeated that winning formula of no puzzles, plenty of shooting but nothing on a par with the likes of Crysis, Half life 2, Cod (choose any of them) or battlefield games.
Halo gives a you a few vehicles, so did BF2 (and planes, and boats, subs) but that was purely online game play, Halo included nothing new in Halo 2, BF2 had an entirely different skin, model list, weaponry. etc etc. Battlefield however had mods, had the vietnam with an entirely different mechanic for flying, all new profiles and skins, and a different physics engine. As did the 2142, once the bugs were sorted you could not only have different kits but the range of upgrades made those kits something completely new. Halo gave you another gun.
Every COD has a different arsenal of unlocks and upgrades, Halo 2 gave you a second hand. Halo 3 gave you an upgrade (shield, speed). ODST gave you less, Halo Reach gave you some more plot and a brief linear flight in a space fighter or VTOL. Even the plots are the same, run and jump and shoot and finally drive a car at great speeds either on a collapsing ship or on a collapsing planet.
Halo didn't define a generation of FPS, it just gave XBOX 360 owners something to play. But you can't compare Halo to anything in other formats. Battlefield 1942, Half life 2, Crysis (not the Crysis 2 port) and Cod:MW pushed and defined FPS for differing reasons.
I own all of the Halo series but each and everyone is the same. I have yet to start Halo 4, but I predict it will have exactly the same plot of run, jump and run and jump, shoot something a lot and then press a few buttons before you drive very quickly against the clock.
Genre defining, no. Peddling the same stuff and having idiots (me included) pay over the odds pricing for the next clone, yes. I also lay odds that graphics, speed, game play and longevity are nothing on a par with the new CS:GO valve have released (not that they follow on their successes) Could be the game, could be the XBOX 360 being just too old now.