Hearing how much everybody loves Siax's Claymores really puts a smile on my face. His powers were always some of the coolest in the series to me, and he's got some really memorable and badass battle quotes. "Moon, shine down!" In particular, is probably one of the most recognizable phrases in the series for me. It's also a great hype generator because you know shit's about to get crazy when you hear that.
I think the best thing KH3 did for the character is that, in addition to getting a second berserk form, he can now quadra-wield his Claymores for huge, widesweeping attacks. Vissually, I remember being in awe the first few times I saw that. Needless to say, I really hope he sticks with his Claymores, or at the very least uses them in tandem with his Keyblade the same way Lea does with his Chakrams. Chances are it'll probably be the latter though.