The +/- gets to the core of what's important in basketball: outscoring your opponent. Because no stat can trace solid defense, blocking out so that a teammate can get the rebound, making the pass before the assist (hockey assist), setting good screens, etc., that's why the +/- is a great stat. Conceivably, a player could be invaluable to a team but neither score nor rebound much.
Another stat to track is points-per-FG attempt. This distinguishes volume shooters that may have a high ppg from efficient players that can get points without a lot of shots. This goes to efficiency ratings, but I do not agree with the statistical formulas for all of that.