"Before we go, there are but things we must first do." would have sounded a lot more grandiose. Correct use of grammar rules the day.
First, my short review of Kohan II:
I picked Dawn of War and Rome: Total War over Kohan II. Kohan II isn't a bad game but it pales in comparison with the other two games, in terms of story quality, longevity, campaign content, gameplay, graphics and sound. In other words, it pales in comparison in every possible way with the sole exception of the musical score by Jeremy Soule.
Gameplay: You can assemble a multitude of armies in cities which depend on what buildings you have constructed in those cities. This allows for plenty of variation in skirmish games as different opponents will undoubtedly employ different strategies and thus utilize variously different units depending on their style and personal mode of play. Combat is fluid and resource management is nil, aside from sending engineers to construct various resource deposites located on the world map. The combat is, however, very mathematical and flanking orders, which are only possible on very large, open maps, are going to be the only variation in bogged combat. Most of the units stand to be rather uninteresting and offer very little in terms of animations or character to gameplay, aside from varying aesthetics.
Graphics: The units look somewhat jagged and simplistic, reminiscent of Age of Mythology but of slightly higher quality. The units are startlingly bland in comparison to those of high detail in last year's TOEE, Rome Total War and Dawn of War and even a game as old as Rise of Nations. Violence and blood spatter is nonexistent, and as such detracts from the game's war theme. Rome may not have much blood, but the animations are more than enough to make up for it. Dawn of War is possibly drenched in blood, and as such, combat tends to be extremely satisfying.
Campaign: This is where Kohan II's main fault lies. The campaign seems to be nothing more than a forethought in implementation. Each of the 25 (!!!) missions consists of nothing more than 'Capture the Town and Kill Everything', which last no more than 10 minutes each, depending on what difficulty you have the game set at. There are zero interludes or character expositions as you complete one useless objective after the next, unlike Dawn of War, which features an ensemble of characters you'll likely find interesting. The voiceovers in Rome, such as those provided by your military advisor, and the speeches before and after each battle provide a lot more character to the game than anything in Kohan II, and most importantly lend an air of authenticity to the game.
Dawn of War might not feature much variation beyond 'killing the enemy' as basic mission objectives but it does offer a multitude of well designed maps in which you may encounter ambushes, secondary objectives, sudden raids and surprises.
Kohan II, as stated before, is by no means a bad game, but its strength lies in multiplayer skirmish and not with any of its single player components. Dawn of War still beats it in multiplayer due to the lobby system, and the moddability of Dawn of War is far more extensive than Kohan II's, so you should just go with that.
All in all, I'd go for Rome and Dawn of War over Kohan II.