Everything else, Tachyon seems better because of his blanket negation and multiple attacks.
To me, against any Xyz deck, this card is hands down amazing. It's a clear replacement for Prime, for non-Galaxy decks, but is it good enough to where it will keep Tachyon from unseating it because of a meta call? But against decks like Kozmo, Yang Zing, and Monarchs, this card will most likely just act as a stool for Full Armor/Dark Matter shenanigans. In match-ups such as Metalfoes, BA-variants, or Blue-Eyes this card can be a blowout taking control of key Xyz monster they make. Please go to 'Search For Decks Containing This Card,' if you would like to search for Decks that contain 'Galaxy-Eyes Cipher Blade Dragon. If it is a Rank 8 Xyz Monster, you can instead summon 'Galaxy-Eyes Cipher Blade Dragon'. However, I want to know how impactful everyone here thinks this card can actually be. TCG official rules for 'Galaxy-Eyes Cipher Blade Dragon.' If you have any questions regarding how to use 'Galaxy-Eyes Cipher Blade Dragon,' go to 'FAQs Related To This Card' for clarification on its usage. Use this cards effect to take control of an opponents Xyz Monster and change its name to 'Galaxy-Eyes Cipher Dragon', then use that monster to Xyz Summon either 'Galaxy-Eyes Full Armor Photon Dragon' or 'Galaxy-Eyes Cipher X Dragon'. In my opinion, this card is definitely going to find its way into the meta in some way, minimium being a bridge to Dark Matter for Dragon decks. One per turn: you can detach 1 Xyz material from this card, then target 1 face-up monster your opponent controls for the rest of this turn, monsters you control cannot attack directly, except this card, also, until the End Phase, take control of that monster, but it's effects are negated, it's attack becomes 3000, and its name becomes "Galaxy-Eyes Cipher Dragon".