Dais: Totally agree. The GBC games tried to some degree to match the spirit their PC counterparts. Even still, they ended up a little simplistic and lackluster (as you might expect). The DS would have given them way more options/potential.
Oh, and Dragon Bone is just straight-up weird. Don't really know what they were trying to do with that one.
avatar: My biggest gripes have to do with the art direction and the interface (and some gameplay issues). Heroes 3 had a simple, attractive interface that interwove a developed, epic artistic style. Each hero not only had a unique gameplay attribute, they had a unique look. A unique identity. Heroes IV throws all that away. The interface, while I wouldn't call it confusing, has a washed out, ugly, parchment appearance that gets too cluttered at times. Heroes can fight (fine), but each faction essentially has two types of heroes to choose from: one set that is combat-oriented, and one set that is magic-oriented. They are otherwise all the same. Hero art and names are chosen basically at random. Heroes can be equipped with gear and consumable potions, but this somehow lacks any of the charm that the artifact system had (there's also that fact that heroes are stronger than most units early, but weaker than most late game, which creates odd incentives).
But the thing that really gets me is that unit animations and portraits are amazingly poorly done. The animations in particular are embarrassingly disjointed and low quality. The unit/hero portraits and town landscapes don't have anywhere near the same epic feel as 3 (hell, or even 2). I also get annoyed that there are only 5 unit tiers in each faction, each tier with a choice of one of two units. Choosing one unit prevents you from recruiting the other. A faction of 5 unit types and interchangeable heroes just doesn't do it for me. So that's it in a rather enormous nutshell.