The murder of Terry in the pilot episode of the Shield is one of those "shock for shock sake" things in TV lore and legends that ended up being a double edged sword: it basically MADE the Shield, as far as making it watercooler talk after the pilot aired, especially after the piss poor promotional lead-up to the pilot (which had Reed Diamond front and center in them). There was ZERO buzz for The Shield until the pilot hit and it exploded online and made the show's rep and elevated Vic Mackey from generic rogue cop protagonist to something much more: the sort of Captain Sensible Villain Protagonist who you can't wait to see what he does next.
The downside is that it basically put a millstone around the show's neck as far as people wondering when Terry's death would come into play against Vic and while the show largely downplayed it until the last couple of seasons, it's to his credit that Shawn Ryan NEVER took the easy way out to retroactively make Terry a monster and justify what Vic did.
(Which is one of the reasons why the atrocious Low Winter Sun was critically and commercially panned: it was a badly written Shield rip-off that featured the lead killing a fellow cop in the pilot but then afterwards made a big song and dance to say it was justified and that the dead cop had done all sorts of evil shit to retroactively make the lead's actions OK. )
And to his credit, after spending the bulk of the run dancing around it, Ryan payed off Terry's death in the final couple of episodes of the show's run in a way that cemented Shield's place in the tv pantheon with one of the most soul gripping finales of the 00s.
That being said.....
The Shield is a show that you could never make nowadays and that's not talking about it's take on corrupt cops or how the show vacillates between condemning Vic and claiming he's a necessary evil. Or the whole "Julian prays the gay away" storyline done to appease the actor.
Also, it's a show that is along the same lines of Venture Brothers in that it was a big deal but managed to avoid a casual/normie take-over of the fandom, so that said fandom stayed clean and pure and avoiding the toxic elements of modern post-Eternal September 1999 internet fandomisms. Part of it was circumstances beyond it's control (the show was infamously blackballed from getting coverage on Television Without Pity due to the fact that said website famously hated FX and outside a couple of shows that got one or two seasons max covered, refused to actively cover the network's offerings) and also, due to the fact that it was opposite the Wire, which got all of the press and fawning praise, leaving Shield and it's fanbase to be protected from the sort of worst kind of normie/casual type fans which corrupt and pervert fandoms.
That said, it's biggest footprint on fandom was the way that Ronnie Gardocki (a minor character in the show's run) became so popular within the show's fandom. To the point that he basically was a sort of prototype for what happened to Derpy Hooves in MLP FiM fandom in terms of becoming super popular within the show's fanbase.