One of the extremely few games that actually deserves the top spot on any strategy/4X lovers shelf.
First thing I suggest is: Do not be fooled by the old-school"ish" graphics, this is NOT another settlers clone, and it is so far beyond what HoMM games are like that I wouldn't even call it a HoMM clone... HoMM don't deserve to be judged on the same terms as Eador.
The amount of micro and all the tiny strategic details is staggering, which brings me to my second point: Give Eador time. This is one of those games that keeps the goodies hidden for a while early on... I was tempted to quit during the tutorial, and actually almost did, until I read some forums that discuss the game further on in the campaign, and at that point I realized that I've no clue what the people are talking about. The first "world"(in game they're called shards, but you don't know this until AFTER you complete the first one) is enough to give a very VERY brief glimpse at how Eador works, it does not showcase all the goodies and bomb the player with pages of notes. No, instead it is very plain, almost simplistic... and that's a good thing in this case.
Why is it a good thing? Because it would be impossible(or nearly so) to explain everything to a new player, and such an attempt would likely make brains explode in most cases. The technology/structure tree is so complex that for a while there was not a way to display the tree, even the maker said that he simply couldn't do it. Today one can find graphical layouts of the tech tree, but even those are split into multiple parts because it's simply too complex to display on a single screen... we're talking around 300(!) structures, on top of that there are spells(8 or 9 different "schools" that also have separate levels), there is a TON of units, numerous variations on heroes, etc... And all these come with a bazillion numbers and stats, so if you like number-crunching, the option is there. If you just wan't to go out an conquer, you can do that too.
And that's why I think this game is basically alone in the "genre." It manages to take the usual turn-based 4X game-play, and seamlessly marries it to a very in-depth strategy game-play. All this without making the game feel somehow disjointed or like a simple mish-mash of the genres... Eador makes it all work! And by adding all the depth the game becomes almost endlessly entertaining.
The difficulty ranges from very easy to nearly impossible, there are 8 or 9 different difficulty settings to chose from. Do not jump in at the Expert difficulty, even if you're able to outplay SCII on the hardest with your eyes closed, or same with HoMM... Eador is tuned at the "old-skool" punishing difficulty, take your time to figure how things work.
Eador is a game for those looking for a serious, deep, strategy game. If you're hunting after the latest graphical shinies this game is not for you. If you tend to get easily frustrated when killed this game may not be for you.
The only reason I give Eador 9/10 is because in 2009 they could have made it MUCH prettier. The graphics look like something from last century... and there is only a single resolution you can play at. But then considering all the other work on this title, I can easily forgive the small purely technological faults. And now that it's available for very cheap and without any DRM, absolutely no reason not to get it. Hopefully the upcoming remake will be just as good.
Just remember, don't expect to dive into Eador on high difficulty right away. And give it some time, at least until second or third world, because in order to keep the amount of new info on a sane level it actually takes that long to absorb the ways of Eador. But most of all, enjoy the ride!