I'm still on HoM&M 5.
It's still very good in the forth mission. I can't help but compare it to a turn-based Warcraft 3 with better control of the camera. HoMM5 is all 3D.
They actually made the game easier to get into, with the tutorial incorporated in the first missions and good use of tooltips.
The single player campaign works like WC3 as you can only play other races once you've cleared the first, second, etc. I haven't played the scenario missions or mp yet.
Combat is a bit repetitive already but it gets better when the hero gains more skills and spells. My strategy so far is simply to gangup on the stronger foes and mopping up the rest after.
Visuals are also very similar to WC3 but more detailed and slightly less cartoony. It's nice to be able to zoom in on the hero and go around him/her with the camera, armor shining in the sun and flags flapping in the wind. Impressive.
The game lags just a bit and some loading times seem to freeze but that could be due to my machine as it is barely above the minimum specs with most settings on normal. It still induced some jaw-droppings already though...
Recommended.