the game offers a wide variety in regards to the unit composition. add doctrines into the equation and that will change the play style more. what limits the way a game will evolve is soviets rushing to pick a doctrine as soon as possible. Soviet commanders offer a high number of tools what will have a great impact on the early to mid game. Late game abilities are also potent, but i don't think those are the ones that have a say in the matter when it comes to choosing a doctrine.
My biggest curiosity at the moment is: "what would be the course of a game if both players would play without choosing a doctrine?"
Most of my 1v1 games i play as ostheer, and recently i've been trying to delay choosing a commander for as long as possible. I've had 2-3 games during the last days where i manage to win without selecting any doctrine. I had a game recently where i was facing a heavy tier 2 clumped up soviet force. I had an army consisting in 3-4 grens, 1-2 pg, 1 mg etc and some p4. My opponent pushed and took the middle vp on kholodny summer and camped the point with 2 at guns 2 maxims and other infantry. As i didn't pick any doctrine, looking at what i had available in terms of unit composition i realized that if i went for jagger infantry for the Light Artillery Barrage will allow me to break his position.(my commander loadout consisted of: Jagger Infantry, Festung Armor and Spearhead Doctrine).
On another note, what contributes to the monotony when it comes to what types of units are called onto the battlefield, is the fact that there are some units that outperform others (i'm looking at two factors:
the purpose of the unit and
the amount of effort/micro/attention you need to invest in the respective unit in order to achieve the desired result ).
Other than that, i also have something else i would like to share with you guys:
Earlier today i had a friend visiting and he asked me to play some 1v1 games with certain constraints of his choosing.
First game on Pripyat Winter:
I had to build a mortar followed by an mg42 and a sniper as the first 3 units, i could not get flamer upgrade on my HT and the only vehicle i was allowed to build out of t3 and t4 was the Stug. Of course i had my ass handed to me but that's not the point. In any case it was an interesting experience.
Second game on Minsk Pocket:
I had to rely only on my t1 and t4 units, t2 and t3 not allowed. I have to say i kinda enjoyed it, as i built panthers and panzerwerfers, units that i didn't have the opportunity to use in 1v1 for quite a while. You can check this one out at:
http://www.coh2.org/replays/5495/playing-with-constraints