I'm always quite surprised when people say that Half Life 1&2 are "Herald of the Decline". There have been countless discussion about the subject, but as far as I can see HL 1&2 are anything but the forefathers of the modern retarded shooter.
Sure, they introduced the "scripted" events, but they were in HL1 quite small, set-pieces that could even be lost or ignored, bar in some specific cases. Let's see....
1) Level Design. Anyone that says that HL1 had "realistic" level design has not played it recently. A ton of HL1 levels have only graphics that make them seem "realistic", but they don't make any sense in a real building. Factories work as platforming sections, parking lots and hangars are well-built arenas with different enemies and enviromental hazards. Even HL2 mantains some of the "game" logic of his forefather. I'll freely admit that they are less creative than Doom Levels, but fights in HL1 are anything but CoD script fests. Sure, the office levels are a tad uncreative, but we can see in Surface Tension at least an attempt to create some interesting situations. HL2 has a lot of very nice fights, that can be approached in a ton of different ways. Even the Episodes have several locations that do not make any sense in a "realistic" way, for example the zombie-infested hospital, but are merely excuses for nice gameplay. Sure, the Episodes also gave us also the terrible focus on the whatevergenericgirlthatIcan'tbebotheredtoremember and to pitiful "emotional engagement" attempts, but Hunter fights and the last Strider battle are very, very good levels. If more shooters where built like that, they would be still fun.
2) Enemy and Weapon variety. HL1&2 have a good enemy variety, and that's already better than 90% of the shooters in the market (without talking of contemporary shooters, that have mostly hitscan mooks and "big foes" fought abusing cover). We have HtH critters, human soldiers, alien foes, flying enemies.... the ingredients are all here. HL2 has less variety, but good fights are still very tense and fast. Nova Prospekt or whatever it was called is still in mah brain as an example of adequate levels with nice gimmicks and different enemies in the same enviroment.
3) Plot, dear god plot. If I read this thread, Half Life seems to be Planescape: Torment. God, Marathon has a more complex and interesting plot than Half Life. And its levels also follow a somewhat plot-dictated progression (you have to board the Phfor ship, for example). HL plot started to became a cancer in the Episodes, when they attempted to sell "emotional engagement" for whatever reason. All the other crap? Xen? Missile silos? Labs? Slave to gameplay. See Opposing Forces and the ton new enemies thrown in to enhance the gameplay options.
4) Half Life 2 is the last gasp of the traditional PC shooter. There is a reason there has not been a sequel: the genre is dead. HL2 with all its problems had still a lot of characteristics of the "traditional PC shooter". I get the impression that it's rather nice to hate it, but we see the last gasp of a dying genre and we point it as the culprit. Rather peculiar. If HL was the creator of the Decline, why we don't have sequels and the Episodes died quietly? And why we have CoD 11 or 12 and countless Halo clones?
Half Life 2 was one of the last specimens of what I like to call "the Second Generation" of PC shooters, that had titles from Shogo to AvP2 to Jedi Outcast to the first Fear, to -sigh- Unreal 2. Different from the traditional and God-given proper FPS of the early-mid '90, but still somewhat creative in design.
Mah stupid opinion though.