The 2004 mix has way too many extraneous sound effects. The original mix had the sound effects placed for maximum effect; notice that when the Star Destroyer fires its big lasers in mid-flyover, there's about a second where there are no sound effects except the rumble of it flying over. The SE mixes, and specifically the '04 mix, are full of extra laser and explosion sounds that don't match what we see onscreen.

Also, the relationship between the FX and music in the '04 mix is odd. Mavimao says the music is buried under the sound effects, but in a way it sounds to me like the sound effects are buried under the music. The music is more audible in the remix (and it sounds too "dry" to me, it doesn't have the added reverb from the original mixes), and more clearly separated from the sound effects (too much IMO; it feels like an isolated score track with sound effects added to it).

What few original sound effects remain are buried under both the music and the new sound effects, or surrounded by so much new stuff that they lose their impact (for example, the aforementioned lull before the SD fires its big lasers - that's one of my favorite sound moments in the original, and it's ruined in the '04 mix because there is no lull anymore, just a bunch of new sound effects). The listener isn't given any opportunity to "breathe", but is instead subjected to a constant barrage of lasers and explosions. There's no focus in the mix, it's the sonic equivalent of those CGI battle scenes in the prequels where there's so much shit going on that you have no idea what to concentrate on.