Hopelessly inefficient and polluting, compared with modern 4-stroke engines, be it diesel or gasoline. Even modern two-stroke are way, way, way behind.

The ONLY benefit of good ole' two-stroke (or modern two stroke) is the weight versus effect ratio. They are simple machines that can be made ligther and cheaper than 4-stroke equivalent. Which is why you find them on motorcycles, snowmobiles and small boat engines.

Recent advances has cut into the niche of two stroke engines. Four stroke for motorcycles are old news. Four stroke outboard boat engines and snowmobile engines are getting more popular and gaining their market share.

Some benefits of four stroke: Much more silent, lower fuel consumption and you have a lot of more torque (moment) at slower speeds (meaning the engine can run slower and still push the boat/snowmobile). The drawbacks are usually higher weight, more complex engines and a higher price.