As far as I'm concerned (and I admit I might be a bit biased since I like the game), I find it balanced/even wether it's vs AI or human (though players' experience can make a big difference of course). Most of the time I just enjoy thinking about all the potential moves and pondering which one I'll chose.
CP will always have the advantage at start (initiative, artillery tech lvl 1, allies joining earlier)but MPPs are more or less equal and Entente have superior navies plus land unit numbers with Russians.
Austria-Hungary isn't that strong and OE is even worse while Entente has many favourable events (though they cost precious MPPs).
So most of the time CP will dominate the early game but their power starts to fade if they can't achieve enough progress while they're on a roll.
As Entente you can play agressive to limit starting german gains or more passive with a long NM game to strangle CP to death. You can also decide to focus on Germany or to try the historical way by eliminating their weaker allies one by one. CP also has several main strategies available.
Whatever the side, IA is good enough to put pressure on you where it can. You can't expect genius or creative maneuvers but it can deal quite well with trench war and the sheer length of the front always allows for some surprises(with fog of war on of course). IA can focus on objectives and force concentration instead of complicated maneuvers but strategic/operational moves are still a big part of the game. Anything you can do better than IA will probably cost you more MPPs to do it.
I also find the balance between MPPs and NM good for all factions. Random parts are ok as well (weather, research, diplomacy, combat rolls/results).
The main problem from old Call to Arms with Germans always reaching infantry tech 1 then 2 too quickly was already solved by limiting infantry research to 1 chit.
The various difficulty/unit experience levels allow you to tweak the balance enough if needed to find a challenge.
I tried playing Entente with max difficulty and Germans are a pain to deal with, you can't waste your forces at the start even if it's tempting or you're doomed. But AI moves still leave some openings here and there.
Overall, you can't avoid making mistakes in this game but you always have a chance to make up for it. But if you make too many you'll often have to take more risks or one last final gamble to turn the tables.
So quite balanced historically wise too as you'll always have several possible plans and many choices but not enough MPPs/units to do everything you want (not even half of them).
I hope that'll help answer your questions ;) .