Yes yes, I noticed that, just didn't mention. My opinion: all of them are great and there are many things to mention why.
HoM&M 3 were great. Though it is kind of easy to get close to important units, because there is no tactic mode for everyone and battlefields are too simple and imbalanced sometimes. Never played 4th one. 5th.. so awesome, because there are 3D graphics and so many new things, especially how hero is actually participating in battle in full strength. 6Th.. well, not like 5th one. Concepts are awesome, art is awesome, graphics are awesome, few new awesome things. I was disappointed when I saw Town view, but still it becomes good with time as you are upgrading it. Also, I like putting effort in hero and it was possible in heroes 5 and even more in 6.