I will skip game advantages, and focus on shortcomings / unpopular design decisions. Top unpopular design decision is battlefield and how movement is handled, so it's basically impossible to perfectly control it. Also with some game knowledge heroes can fairly easily get extremely powerful so army tends to be less important than in previous titles. One of biggest shortcomings for singleplayer is fairly dumb AI - it can be challenging on properly designed map, or when you try to give AI better vision via extra objects near AI, tune AI priorites of some objects in map editor etc. General shortcoming for both singleplayer and multiplayer is no random map generator and no legacy modding scene so there is no advanced "HD mod" for H4 like it was done for H3. That means lack of QoL fixes and multiplayer extra features like simultaneous turns. One upside is that very recently (miracle happened wow) H4 got some modding attention, and patch to Albyx mod just got released. I did not try it yet but it apparently drastically improves AI. And it's possible to run that AI overhaul without rest of mod content if somebody doesn't like custom balance fixes etc.
