I've got a few boxes now on 5.2.5 with no displayed issues although I was a bit worried about the release note item:
"Administrative access to the FortiGate using HTTPs and SSLVPN with the second WAN interface may fail upon upgrading to 5.2.5."
This is a little ambiguous - are they saying that if you use a combination of HTTPS admin on wan2 ( could this be any 2nd wan interface or wan2 itself? ) and SSL VPN on the same wan2 interface that you could have a problem?
Otherwise, besides some 60D and 90Ds having high CPU on occasion on 5.2.3 ( solved with 5.2.4 ), no other real issues.