On the surface, Microsoft is lagging behind its big rival in the videogame business. But the company is succeeding where it counts.

Such was on display Sunday as the company showcased its coming videogame offerings as part of the annual E3 conference in Los Angeles. The company previewed 50 game releases, 18 of which will be exclusive to its Xbox console. The latter included major new iterations of “Halo” and “Gears of War” that have been marquee franchises for the company but haven’t seen a significant new release in at least...