Valentine and ET are similar in that they can both clean the defensive glass like PFs and can pass the ball at high levels, but they are very different types of players.
ET is a primary half-court shot-creator. He can dribble and create against pressure a la Pierce. His problem is that he can't shoot or score like Pierce.
Valentine is a secondary half-court shot-creator a la Draymond Green or Boris Diaw. He doesn't have the smooth handle to operate in isolation like ET, but his vision and intelligence allow him to serve as an excellent secondary playmaker when someone else does the initial hard work of breaking down the D. On the fastbreak, also like Green and Diaw, he can serve as a primary creator, taking advantage of the inherent fluidity of transition to find good scoring opportunities. Great advance passer.
What makes Valentine unique is that shooting ability. ET of course can't shoot a lick, and Green and Diaw have always been mediocre from distance. But Valentine can shoot with accuracy and volume, spotting up, off dribble hand offs and off screens. That could make him far more dangerous than Green, Diaw or ET offensively.
I think he has a chance to be one of the top 5 players from this draft. The big thing potentially holding him back is his D. But his agility graded out very nicely at the combine and guys with his physical profile (Wes Matthews, Landry Fields) have done pretty well defensively .
For me, it's Valentine or bust beyond the BK pick. If he's gonna go higher than the Dallas pick, I'd happily trade that pick plus #23 and any 2nds to go up and grab him.