To be perfectly frank with you, Over The Top: WWI is Battlefield, Hell Let Loose, Holdfast, etc. having a loud and dirty baby. Having spent a decent amount of time in the trenches, I will provide you with my unbiased analysis and opinion on this game.
The most amazing thing about this game is a mixture of the sandbox gameplay and huge numbers of players per battle. You are not running around a fixed map trying to eliminate the enemy. In case someone is annoying you by shooting from some farmhouse, feel free to blow the place up. Need a quick shelter? Grab a shovel and dig one!

Map is constantly changing depending on actions made by the players. There are craters left by explosions, shifting front lines due to the actions of players building things or destroying. The game is a sandbox and you have full freedom. One second, you are charging the trenches with a bayonet among hundreds of others. Another second, you find yourself in a new experimental tank with ten people in there. Or you could be just whacking people with a baguette, who knows.
Open Voice Over IP is just the cherry on top. Imagine listening to a couple dozen people raging over VOIP about everything possible, playing a historic march, shouting as they charge the enemy line. It will probably drive you crazy but in a good way.

In addition, the game features a great offline sandbox mode, where you can fill the server with bots and enjoy the process at your own pace without being bothered by humans.
Again, I have to warn you, the game is a sandbox and therefore it is far from perfect and polished. It is an indie game and that can be noticed from the very beginning.

First of all, you should prepare yourself mentally to the following:
Overall, there is no doubt in my mind that Over The Top: WWI deserves its place among the best sandbox experiences. It is a great opportunity for casual gaming in huge maps, both massive online and offline battles.

Moreover, the lack of seriousness in this game is a huge plus. Just give players a bunch of weapons, drop them in a mess and see what happens. If you are tired of contemporary games and looking for something light and fun, this title is absolutely worth your money.