ST:TMP:TDE, fixed most of the pacing problems which the theatrical release suffered from. It also fixed some seens that seemed unfinished. The recut of the movie actually earned a PG rating, as opposed to the G rating of the theatrical release.

For example, when V'Ger's attack upon the Enterprise with one of the devices which it used to destroy the Klingons, is aborted, in the theatrical realease the music and sound effects build, then the device simply dissapears from the viewscreen, and the music and sound effects ackwardly fade out. In the Directors Edition, the music and sound effects build, and then cut to an exterior shot of the device disapating as it approaches the Enterprise. This leaves the scene feeling much more tense, and finished.

The scenes of the Enterprise flying around V'Ger's spaceship actually seem to have a point to them, as we actually can see the ship, and get a true sense of scale opposed to the Enterprise. However, this may just be part of the difference of having watched a dirty VHS pan and scan transfer of the film (with 12 extra minutes!) in the past.

There are also some seemingly unnecessary changes, such as the path between the Enterprise and V'Ger itself forming as Kirk & Co. are walking on it. However these do not distract from the movie.

IMHO, the most impressive effects change is the final effect shot of V'Ger's ship sitting over Earth before it explodes into a new level of consiousness. This effect incorporated the original shot of V'Ger's explosion with the Enterprise flying out of the light, with new elements preceeding them.

Overall, the new effect are subtle, and if you hadn't ever watched the movie before, you would never pick them out. But it is the changes in pacing which ultimately make this a much better movie.