There was a noticeable gameplay impact with weapon reach in Diablo II. I've noticed the same impact in Diablo III. In general though, weapon reach importance varies depending on your play style.
In a strictly melee playstyle, weapon reach will determine the 'radius' of your 'circle of death'. I much prefer a higher attack speed w/ a crowd control skill in these instances. However, when ranged damage dealers arrive, a melee character must chase down a fleeing ranged enemy, thus making a longer reach weapon more useful: The chase is shorter because the weapon reach will pick up some of the distance. Since the longer reach weapons usually have higher single-smack damage, the fleeing enemy will usually pause slightly for hit recovery, thus almost always ensuring followup strikes.
If your melee character is highly mobile or has a high movement speed, weapon reach takes second chair to an increased attack speed.
Obviously, this does not apply to ranged damage characters.
In my opinion, higher attack speed is key: Since crowd control is going to be used ANYWAYS... one may as well benefit from applying damage constantly (more enemy hit recovery) and triggering more 'per hit/strike/kill' effects.
Spoken as a DI, DII, and current DIII player that plays both melee and ranged characters. Playing a dual wielding Barb now... dos daggers :)