Any major changes in code from 11.2.1 11.4.1 for BIGIP?

11.4 introduces significant changes. HTTP classes are no longer used, and have been replaced by local traffic policies. See some details here:

http://support.f5.com/kb/en-us/products/big-ip_asm/manuals/product/asm-implementations-11-4-0/20.html

When upgrading, you may need to take some manual steps because certain configuration elements will cause the upgrade to fail:

http://support.f5.com/kb/en-us/solutions/public/14000/400/sol14409.html

Thank you for your input. Is any behavior changed going from 11.2.1 to 11.3?

Thank you.

There are some new features, but no major feature changes like moving to 11.4 would have. You can read more about 11.3 for ASM here:

http://support.f5.com/kb/en-us/products/big-ip_asm/releasenotes/product/relnote-asm-11-3-0.html