Here is a link that explains win shares: LINK
It's another metric that is a little weird. It focuses on points scored/allowed to produce a total win share (offensive + defensive = total). Once again, it fails to consider context at all and focuses largely on the black and white of points.
Look at last night's Heat/Bulls game. Lebron was 6-17 (with 11-11 on free throws) for 25 points. Effective but inefficient. Yet, it was Lebron knocking down two crucial shots in crunch time that sealed that win (along with another three pointer from Cole for good measure). Yes, Bosh and Cole dominated throughout the game, but when they needed it most Lebron made it happen. If I had only one win share to give--I'd give it to him.
I also believe it is based on the team's total wins so a team that wins more has more win shares to give. This seems imbalanced right off the start as no credit is being assigned for losses (which should be deducted from a player's win total to be fair) and there is no basis for how the team as a whole affects one player's individual score.
It came as no surprise when looking at the leaders board that there are only five players from losing teams in the top 50 for total win share. Thaddeus Young (33), Amir Johnson (34), LaMarcus Aldridge (36), JJ Hickson (42), and Ryan Anderson (47).
The name that stands out is Aldridge, of course. I would feel very safe assuming Aldridge's score increases if he takes Chris Bosh's (20) role on Miami. Players that scored higher than Aldridge: Blake Griffin (10), George Hill (12), David Lee (18), David West (19), Tiago Splitter (25), Al Jefferson (28), Jose Calderon (31), Ty Lawson (32), and the aforementioned Young and Johnson above at 33 & 34.
This leaves me wondering what exactly does this stat tell me? It tells me whether a player was part of a good team or a bad one mostly. Although, we must also be careful about the "good stats/bad team" guys.
So, what I see is a statistic that is heavily based off of team scoring statistics being applied to individuals to try and forecast a player's contribution to a team. Further, it becomes largely useless when trying to convey that score to another team--namely, the Rockets.
If you want to take Millsap's win share score, subtract our PF's collective win shares, and then add that to see what you get then I guess you can. Without including Delfino, Patterson, or Morris that score is 5.5. So, Millsap gives us +2.1 wins. For $10M that's not very much, is it?
In my opinion this stat is fun to look at, but has very little value--even within the context of it's own team as it does not consider a player's contributions outside of scoring and applies points allowed indiscriminately.