Baroque and earlier music are easy to read (sometimes not) but helluva hard to perform as the way it was intended. The majority of information needed for a good performance isn't written in original sheet music - as the pro baroque player was well versed in music, most of information and customs weren't written because it was redundant - so usually you need to figure out all by yourself (or by listening to performances or reading books and papers about it) 'cause this ain't anymore our sociocultural context.
Aside this, we're dealing here (Goldberg) with an idiomatic writing for a different keyboard instrument - harpsichord with double manuals. Piano and harpsichord are similar only in keyboard layout and having strings within - all other features are very different. The sound mechanism is completely different and demand different technical gestures when playing keys on each instrument.
Harpsichord doesn't have real dynamic changes - when a key is pressed, it will sound at the same volume. But it has 2, 3 or more different sets of strings (called registers) and changing registrations will affect dynamics and tone. Apart this, there's special fingering techniques to emulate crescendos and decrescendos (aural illusion). Even if you're not supposed to use these fingerings, the dynamic changes aren't written, so you need to know when do or do not these by rhetoric.
Ornaments and improvising are a completely new level, we cannot explain even the basics in a short post here. And you're supposed to use this in every Bach's art piece. Or Handel's. Or Telemann's... you get it.
Playing polyphonic passages requires an additional effort: make each voice sound well separately and unique when grouped together. Fugues and canons provide more difficulties because, to assure coherence, you need to play the same articulations when the same subjects appear - sometimes, there's situations when you cannot physically play what is demanding, so you need to understand the problem and provide solutions.
Another "problem" when performing Bach is harmony clarity: you usually are within an harmonic context that is cristal clear. One wrong note or even a note played non confidently and you will sound wrong - like as someone painting the sea with only vivid reds at a midsummer day marine painting. Every listener, even not trained, will catch instantaneously and intuitively every error.
To me, Goldberg Variations, The Art of Fugue and Musical Offering are the pinnacle of Bach's music, along with concertos and strings solo music. As I said, looks easy on paper, but it is hard a lot to play well.