Apex Legends is simultaneously all the modern upgrades for FPS done right mixed with a number of "hard" downgrades by the developer to hit that sweet spot between ultra competitive and casuals mixing it up. Things like removing wall running and Titans, while controversial, shows the ups and downs of the FPS genre and success where the masses can take it to the pros.
Halo gets lots of game balance/focus elements like rockets or OHK snipers etc where Apex/Respawn have downgraded a series of such things in favour of balancing movement or weapons or damage or solo vs team etc. Apex is the sweet spot, no other FPS is as on the money when things are going smooth.
All online FPS are smoke and mirrors bullshit based on latency making it even work when playing MM. Apex just has that killer sandbox with classes so finely tuned by comparison to other games out there. The ping system, the squad system, the revives, the respawns, the map indoor/outdoor play, the characters stacking abilities etc. The brilliant moments that come from Apex e.g. out 301/wingmanning in a 1v1 or kidnapping an enemy with wraith or bamboozling with Mirage while your team attack from a Revvie totem etc. The modes of support e.g. winter events, TDM, control, 6v6, trios, ranked are all too good.
Honestly Apex is what Halo should have become for some modes or releases. For replayability few games stand up against Apex; I consider Halo 2 & 3 there but none of the others. The same goes for many other FPS franchises, they just don't have that sustain and it factor around me wanting to play time and time again.