Hi!
Is someone else having problems with 2D colliders and OnTriggerEnter2D. My game does not detect Triggers with the new version.
We are currently looking at bug reports submitted for this issue in 5.3, you can follow the conversation here: http://forum.unity3d.com/threads/unity-2d-trigger-box-colliders-not-working-on-5-3.372615/
There are a couple of fixes that have been verified against all reported bugs. They are going into 5.3.0p1 and 5.2.4 soon.
The issues started in 5.2.3p1 and were carried into the 5.3.0 release unfortunately.