I've been playing it, and I'm impressed. I think they have a good mix of WW1 equipment and the battlefield gameplay. Obviously it isn't very realistic, but in terms of a Battlefield game, enough is new/changed that it doesn't feel exactly like Battlefield 4.
As for the chemical warfare, so far in the beta (on only one map and not all equipment can be unlocked), there are gas grenades, but everyone has a gas mask and the gas slowly does damage if you don't put the mask on. But its obvious when/where's there's gas, and its easy to put the mask on. The tradeoff is when you have your mask on, you can't look down your sights. So throwing gas still has an effect on the enemy players.