HOMM4 has undergone some changes from the previous titles in the series.  I personally have not played all of the series, however after playing the game, and attending some newsgroups, this should give you a good feel what is expected in this new edition to a very popular series.

In HOMM4 the basic gameplay hasn't changed too much.  Gather resources, construct buildings, recruit creatures, develop your heroes, Take over enemy towns, etc. Some of the strategy involved in accomplishing these tasks has changed.  For example the heroes you pick, (and now you can have more than one), don't just sit back and cast spells from the cheap seats while your troops get slaughtered.  Now they are right in the heat of battle targeting the enemy and actually taking damage as well.  So yes now you have to protect your heroes if you want to see some high levels.  There are also different classes of heroes that affect the skills one can learn.

With the new caravan option you can easily transport armies around the map without having to watch over them.  It happens automatically and the time taken is dependant on the distance between cities.  You can also split armies without having to have a hero with them.  This works great for speeding up the gathering of resources, but you will need a hero to capture most buildings.

In Battle, I found the gameplay a bit difficult.  There is no longer a grid which you can easily place your troops. This makes it some times confusing and you may find yourself putting them in the wrong place from where you intended.  There is no message text to let you know what spell has been cast either.  I did like the counter attacking enemies as well as, the roaming ones.

Some of the other new additions to game are, but not limited to:

• 6 new challenging campaigns in a new Might and Magic world.

• 5 schools of magic: Order, Life, Nature, Chaos, and Death.

• Complete quests involving over 400 individual adventure structures.

• Choose from 11 starting hero classes, each with unique abilities, and progress to 37 advance hero classes.

• Command over 60 fantastic creatures with extraordinary new combat abilities.

• The new isometric engine immerses you in the excitement of adventure and combat.

The graphics are quite nice.  Though its pretty much 2D, they are quite an improvement overall from the previous titles.  The buildings and characters are nicely rendered and you really do notice the attention to detail.  Is it eye candy?  Well not really but it’s the gameplay that will sell this title.  The Graphics are a nice plus, but not the reason to go upgrade your video card.  Games of this genre usually do not rely on graphics anyway.  

Newbies to the series may find the gameplay and interface a little daunting at first, more like the first two hours.  After speaking with experienced HMMO3 players, the consensus shows that even veterans may need an hour or so to navigate the new interface and adjust to the new changes.  Don't let that turn you off.  You didn't learn to drive a car in 15 minutes.  Once you get it down, the real fun begins.

All in all this is a must have for HOMM fans and if you are new to the series, you couldn't pick a better time to get started

Install: Easy
A no brainer

Gameplay: 8.5
Some of the new enhancements will have devoted fans learning the interface all over again but should only take an hour or so to get a good understanding of what is going on.  For those who are new to the series you might want to give it a couple of hours of trial and error to get a full understanding.  Truth be told, it's worth the time.

Graphics: 7 
Much better than the earlier titles but nothing earth shattering.  But for turn-based fans, this is not actually a requirement to enjoy the game.

Sound: 7
Sound effects were ok.  The music wasn't bad, in fact was quite good, but in some instances didn't quite go with the gameplay.

Difficulty 9
This title is quite challenging and is very tactical.  Multiplayer will provide even bigger challenges once the update released.

Concept: 8.5
A long awaited addition to a series with a strong following.  The new changes that were added made the game very enjoyable.  A nice blend of turn based strategy, fantasy, and RPG elements.

Multiplayer: 
Not available yet but is promised in an update which you can download at a later date

Overall: 8.5
A must have for fans of the series