The first few were really good on console. I played the first one on PC as well and there was definitely something missing with mouse and keyboard controls.

You have to remember that most FPS on consoles were pretty terrible back then (e.g. Medal of Honor series), and there was a lot of experimentation to try and find a control scheme that didn’t completely suck, along with just the right amount of aim assist. Other devs were still wrestling with that into the Xbox 360 era. Sony put so much effort and money into Killzone, and it wasn’t anywhere near as good as Halo.

Plus, split screen co-op made it very popular. It’s one of the few games to keep that into the modern era as well.