I think that is a matter of opinion. Weapons tend to only be memorable if you loved using them. For people that started the Halo experience with Halo 4, I'm sure weapons like the instant kill Binary Rifle with a never-ending laser and the ultimate camper tool, the Boltshot, are highly memorable.
I personally really like the Binary Rifle, it's a One-Shot Wonder, but balanced because of the low ammo cartridges and the laser it emits when scoping scoping. (And let's face it, it's next to impossible to get a snapshot with)
I think Halo 4 featured many memorable weapons, UNSC, Covenant, and Forerunners alike. I'm hoping Halo 5 has its share of awesome weapons as well.
[Also, how is 'Grenade Launcher' a better name than 'Scattershot' or 'Boltshot?']