The big difference between XI and XIV combat wise at least is all about pacing.

XI: Use your skills reactively, adapt to the situation. Combat was much slower paced focused around auto attacks all skills were only (Often long) cooldowns, some people don't like the slow pace.

XIV: Use your skills ALL THE TIME, there is little to "React" outside scripted events that make you step outside the painted death lines. The only real difficulty is if you continue to optimize your DPS while running around the field.

Personally I enjoyed the slower paced more methodical combat. I'm not really a fan of ramming my 1-2-3 macros switching it up with a 4-5 every once in a while making sure all my cooldowns are used and not really thinking about the combat itself I'm focused on the skillbar.