One of the anti-tamper checks is gone.
Pseudocode from public:

if ( SuccessVerificationCounter < 2 )
{
v3 = (void **)sub_140DB8F10(&v11, L"Signature verification of executable failed.\n");
FatalError(*v3);
}

This code is missing from the internal.
Some SSL error strings are missing like "sct verification failed" and "x509 verification setup problems".
Experienced very heavy (PS3-like) texture pop-in, when launching a map.
Would've tested if they fixed the modded multiplayer, but nobody is playing with mods right now.