PC Gamer recommends the Long War mod for XCOM 2:

The Long War 2 mod is a must-play reinvention of XCOM 2

New classes, weapons, and a reworked campaign map successfully refresh this excellent strategy game.

The word 'mod' undersells The Long War 2. 'Mod' implies an aesthetic tweak, a UI correction, a new weapon perhaps. In fact this is XCOM 2 as developed in a parallel universe. The Long War 2 does add lots of new weapons, classes and skills, but all these service a set of bespoke design aims that turn XCOM 2 from a survival strategy game into a gradually paced army and territory management sim with expanded combat encounters.

For players that have mastered XCOM 2's story and power arcs, or now find them predictable, Long War 2 is an essential download. The mod forces you to break out of your habits and re-engage with the game again at the most basic level. Even soldiers are valued differently. You can field up to ten in a mission, and you start with a large roster. Consequently, losing agents isn't the body blow it can be in trad XCOM, and you have more room to experiment with ability and weapon combinations across your force.

Your whole stance as resistance commander feels different to ordinary XCOM 2, which forces you into a reactive position with must-fight emergency missions. In The Long War 2 missions are more like leads that you can choose to spend time and resources to follow up. Ordinary missions are precluded by an infiltration period that asks you to devote a squad to a location for a variable number of days. If they achieve a high degree of infiltration (represented by a percentage marker that ticks upwards with each day), they face weaker forces in that mission.

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The changes bring a dose of 4X strategy to XCOM 2. This slows the pace considerably—this is the Long War, after all. This dilutes the impact and drama of an XCOM 2 campaign to an extent. The way the core game gives you a narrow stream of high-stakes decisions is one of the reasons I loved it so much when I reviewed it last year. However I've found it fascinating to see how XCOM's core mechanics work in this new context. The Long War 2 is a thoughtful and effective reworking of the XCOM 2 formula, and the new weapon, class and mission additions are slick and well-integrated—they could have come from Firaxis.

Speaking of Firaxis, it's great to see studios work with modders, particularly in instances where the mod team wants to substantially rework the studio's original vision. The result is a neat Earth-B take on the concept that unlocks hundreds of hours of extra playtime. The Long War 2 is out now, and it's free.