I liked Killzone 1 a lot, the second one however... had one of the best moments of the franchise like the Radec boss fight but overall didnt surprised me as much, and i didnt liked the control scheme, plus the multiplayer was... not my favorite because im not a fan of multiplayer games where you have to empty an entire magazine of bullets on one player to just kill him.
Killzone 3 however also had some great moments (not anything as hard or rewarding as the Radec boss fight), but it was more consistent (in quality as in it doesnt become as repetitive) and it had more variety on the levels, including some vehicle levels, and i really liked the control scheme this time arround, (and yes the control scheme is like COD, but who cares thats the best scheme for an FPS), so i ended up liking KZ 3 more than KZ 2.
havent played Shadow Fall and i dont know if i will, maybe it will be on PLUS some time on the future.
EDIT: and in KZ 3 you didnt have to empty the entire guns magazine to kill another player which to me was a huge improvement over KZ 2, this time you only had to shoot half or maybe a quarter of your magazine to take another player down, which is more in line on the type of shooter that i like.
