The Biggest Game of Lebron James' life...was awful.

Dallas won by 9 points, which is 10.4 points per 100 possessions.

I split credit of the team's point margin in half, adjusted for pace, quality of opponent, and home-court-advantage.

Dallas played like a +4.98 team
Miami played like a -4.98 team

TOV%=percent of a player's possessions that ended in a turnover (basketball-reference.com's boxscore).
ORTG=offensive rating. very complex measure for efficiency
DRTG=defensive rating, similar to the above.
+/- = Plus-Minus rating, as tabulated by ESPN's box score. It shows the change in point margin while a player is on the court.

Raw est APM(100)= an estimate (using the above) of how much a player impacted his team's point margin per 100 possessions.

Adj est +/- (G) = an estimate of how much a player impacted his team's point margin per 100 possessions

team	Starters	MP	TOV%	ORtg	DRtg	+/-	Raw est APM(100)	Adj est +/- (G)
DAL	Jason Kidd	39.87	30.4	139	115	13	4.27	3.17
DAL	Tyson Chandler	38.67	0	150	117	14	3.03	2.08
DAL	Dirk Nowitzki	39.62	8.2	125	119	14	2.46	1.66
DAL	Shawn Marion	34.03	15.4	80	117	21	1.85	0.99
MIA	Mario Chalmers	23.45	12	175	128	-1	0.53	0.55
MIA	Mike Miller	23.20	16.7	143	128	0	-0.29	0.15
MIA	Juwan Howard	5.82	0	200	134	6	-0.02	0.07
DAL	Jason Terry	30.48	13.4	146	123	1	0.44	0.00
MIA	Udonis Haslem	33.00	0	140	131	0	-0.78	-0.13
MIA	Eddie House	3.47	33.3	0	95	3	-3.85	-0.23
DAL	Jose Juan Barea	25.65	8	146	126	4	0.00	-0.24
MIA	Joel Anthony	16.20	0	200	135	-9	-1.55	-0.32
DAL	Brian Cardinal	9.62	34.7	106	114	-7	-2.42	-0.57
DAL	Ian Mahinmi	8.1	0	123	123	-3	-3.70	-0.70
MIA	Dwyane Wade	34.45	18.8	126	124	-13	-1.74	-0.82
MIA	Mike Bibby	15.40	33.3	62	134	-7	-4.74	-1.33
MIA	Chris Bosh	39.38	20	113	131	-13	-2.24	-1.35
DAL	DeShawn Stevenson	13.97	0	133	127	-12	-4.44	-1.42
MIA	LeBron James	45.63	16.8	98	131	-11	-2.23	-1.56

(Here is a quick spreadsheet that explains how I currently estimate APM.)

James played nearly every minute of this game, and didn't really succeed. Per-possession, Bibby had a much worse game, however.

EDIT: By the way - these numbers are based on a prediction of these ratings.