I had an unfavorable impression at first for many of the same reasons as the OP.
After doing the tutorial 'scenario' completely my opinion of the potential for the game was greatly increased. The GUI was 'revealed' to me more, opening up more and more features and possibilities.
I was thinking exactly the same thing about the units - just melee and ranged, basically, with different names for different realms. However, it's in looking at the differing purchase costs, maintenance costs, and any special characteristics for those units that the great variety really jumped out. Each realm has a limited number of unique and elite units.
Example: one realm (I think Iron Barony) has very cheap goblin mercenaries available, and they are available immediately since they're mercenary, but the maintenance is very expensive. So it's impossible to keep an army in the field made up of those mercenaries for more than one or two turns. The player has to really use them wisely.
another example: I think it is the Cloudfels realm that has a relatively inexpensive but very powerful three-headed wolf unit (forgot the name of it), however, it cannot leave it's home province.
Another realm, one inhabited by elven people, has a unique unit that is able to imprison enemy units under certain conditions.
There are many, many nuances to the basic unit types like that.
Another area of the game offering great variety is the realm-specific goals. One that really has me intrigued is the realm Ariselle (sp). It's kind of modeled after Great Britain, in that it is an island realm, has a powerful navy, and diplomatically (when the AI plays it) it can never be allied with the most powerful realm in the world. In fact it will actively oppose the most powerful realm. Another unique realm is one that is only played by the AI, and it's kind of modeled after Switzerland - it's neutral, is the center of a League of Nations type thing, and if attacked by anyone, is immediately defended by all others.