I installed it on one of our test boxes and the installation hit a few problems, first gcc/ld failed with a missing libstd++.so.5 error, had to install another compat library and the linking retry worked fine.
Secondly dbca failed with a boring "TNS: lost connection" error. Quick look in the log files showed that sqlplus died with a missing libaio error (yes, the pre-reqs should have checked for this and warned if the RPM was missing). After installing the RPM I ran dbca again and it finished without problems.
10gR2 pretty much feels like normal 10g on the surface, the cool stuff is deeper down. I'm going to try out some of the new features later today or tomorrow, and no, I'm not going to write any stored procedures in VB. ;-)
One thing I reflected over is that 10gR2 feels a bit "lighter" than 10g, it uses a tad more memory but feels faster on my quite slow 800MHz test box than 10g does.
View the 10g Release 2 documentation library.
Command to check for the two missing RPMs (required on my FC4 system):
rpm -q compat-libstdc++-33 libaio