render your work often, and play it in winamp or so (even better: burn it on a CD and play it on a stereo).
you should feel better what's lacking and what's to be kept.
Amen...
Don't sweat the detail too much. Render tracks to CD, thnk of them as "demos" sit on them for a few days then listen back to them away from your computer. It's too easy to get lost in tweaking and general sound design/dicking about.
Apple iMac (OSX 10.5.2). Ableton Live 5.2.2 with Operator.