Eddington gravity

Eddington proposed a relativistic model of gravity where the gravitational action \(S_g\) had the form \(S_g = \int\mathrm{d}^4x\:\sqrt{-g}\:R_{abcd}R^{abcd}\) based on the invariant curvature \(R_{abcd}R^{abcd}\). what would be similar to general relativity and what would be different?