Infantry dies FAST. Even charging against simple trenches manned by regular infantry means a whole battalion/unit will disappear in an instant. Now imagine doing the same when said trenches are supported by Maxim guns and while enemy (heavy) artillery is dropping shells on you. This is hell and losses are going to be terrible, as is apprioriate for the setting.
And that's only the beginning of the game - I have yet to explore bombers, tanks, gas, flamethrowers, etc. So the tools for breaking the stalemate and to provide strategic variety are there.
Some decisions are questionable though: in order to allow aircrafts to shoot down observation balloon (that provide visibility) you have to invest a bunch of points into tech tree, despite the fact that aircrafts (with machinegun on them, to fight other aircrafts!) are literally the first aerial tech you unlock.
The game is complex, in a good sense.
You have gold and supplies. Troops' losses are replenished with gold. Equipment (such as tanks, aircrafts, etc.) is bought with gold (and can be lost permanently, unlike infantry). Supplies can be bought with gold. So having gold is good. Which means you should conserve troops, because losing too many troops will cost you money. But to conserve troops and gain objectives you need to use supplies and supplies are limited (you get a certain amount of both gold and supplies each turn), so using too much supplies isn't without consequences either, because it can eat into your strategic reserve of supplies.
This creates a certain set of checks and balances you have to take into consideration, because each army has a limited amount of "local" supply per territory and attacking enemy territory also requires a certain "tax" of supplies (depending on the size of the attacking force), so you can't attack willy-nilly. Also, both attacking and defending tires out your army, meaning that attacking the same hex will make it easier to break troops' morale, but open you up to the same tactic when it's your enemy's turn (battle fatigue regenerates at the start of your own turn).
Another interesting aspect of the game are persistent trenches - each province is a hex. Each hex has 6 sides. This means you can, potentially, have six maps for any given hex. And each unique map will have its own set of trenches that was left from any previous battle fought between Hex A and Hex B. This means each fight will be that much harder on account of having to find a way through even more complex maze of trenches. "Trench warfare" is name of the game here.
Also, each battle is on timer (20 minutes). You can pound enemy lines endlessly with artillery (assuming you have supplies for that) and then attack, but this will leave you with less time to capture all objectives. Of course, you don't have to take ALL the objectives in one battle. But until you do, you won't be able to breach the defenses of the region and take control over it.
Because each region has a bunch of stars to signify how well fortified it is (from 1 to 5). Taking a place with 2 stars will require two "total victories". While normally I don't like the idea of timers, in this case it's a pretty good way to encourage you to act suboptimally if you want to capture as much ground as possible. Which means losses will likely be horrid.
This really helps to capture both the idea of a stalemate and that each "inch of ground" comes at a certain cost, and even capturing one well-defended point can be a minor victory that's a good stepping stone to greater victory in the future. At the same time you can see "Great Victory/Sweep" info, while looking at the casualties and realize how phyrric this victory was in terms of resources (men/gold).
It's good to see that the AI can offer surrender and ceasefire terms when it deems it appropriate to do so (which you may or may not accept), so you don't have to always play through all 20 minutes very time you go to a battle.
Negatives?
AI can make questionable decisions sometimes (such as spending all its troops in a counter-attack, leaving its positions pretty much exposed for your own attack, if you have spare troops yourself).
Some tech is strangely placed - you have to research balloon hunting missions somewhat deep into the aerial tech tree, despite the fact that the very first tech unlocks aircraft that are capable of shooting down enemy aircrafts, I guess this is for balance reasons but I still don't like it.
Troops' movement can be weird sometimes when it comes to moving via trenches and it sometimes can result in lossing troops unnecessarily, because they take a "shortcut" that ends up with them walking into enemy gunfire.