One of the biggest complaints Ive heard against the iPod or iPhone as a music player is the lack of a working adjustable EQ. Quite simply, this app changes that. The fact that it uses the iOSs native audio playback, allowing it to continue when locked and be controlled by remote, is the stroke of genius that makes this app superior to the others. Infinite manipulation points for the EQ are nice, albeit unnecessary for most well-recorded audio. Good for adjusting those concert bootlegs, though!
If I was to change only a single thing, though, I would polish up the app interface. It is functional, but could afford some visual improvements, and a slight toning-down of the gaudy splash graphic on opening. The play/rewind/forward buttons are a bit too small, and the EQ button is tiny. Several of the window elements, including these buttons, seem just a bit cramped into their space. The volume slider and AirPlay button sit awkwardly across the divider between the art and the controls.
Functionally, though, the app is absolutely great. With just a few visual fixes, it could be amazing.
MacMan about Equalizer Pro, v1.0.1