Jagged Alliance is a bit less hardcore than XCOM's difficulty, it's pretty easy to cheese when you understand the AI or how the stats/traits work. Jagged Alliance 2 has been more or less the definitive game for the series for 24 years by now, with the Patch 1.13 mod serving to grant it life beyond it's regular scope as it vastly expands the game content in all kinds of ways. The basic experience unmodded is a bit XCOM adjacent though it's not quite 1:1, JA2 actually does include some weird alien bugs you can run into if you play it with Sci-fi Mode enabled literally because of how popular XCOM was at the initial time of release, they felt like they needed to have at least something in the game as a kind of nod.
The 1.13 mod and the various tweaks for it turn it into a completely different type of experience and can really test your tactical and strategic mastery of the game. Tons of new weapons, attachments, armour and equipment, mechanics and features. Roving armour battalions, enemy spec ops, undercover hitmen infiltrating your captured towns and trying to dome your mercs ASAP. Capturing enemies by force with handcuffs, breaking their morale with suppression until they surrender, building sandbag walls to provide cover to entrenched machinegunners and mortar teams, reaction-fire sniper-spotter team set ups. Maintaining food/medicine/ammo logistics to keep your lines supplied as you push, fighting off 100+ enemy counter raids with a squad of 6 retards, maintaining the morale and support of the Arulcan populace to increase the profits you gain from holding mines and earning enough trust in strategic locations to run improved shipping operations out of the country to multiply your income so you can afford more guns and ammo.
All of this, variably tunable through pretty simple xml and tools, turning on and off what you don't want, adjusting it to suit your tastes as easy or brutal as you want. I've unironically played this game longer than some people on this site have been alive and I still come back to it at least once a year for another several week long campaign playthrough that takes at least 100 hours minimum. The long awaited Jagged Alliance 3 is coming out today, ostensibly sometime within the next 2-3 hours. The first numbered, true sequel to the Jagged Alliance franchise and the first one of these types of franchise continuing games to show enough promise that original series designer Ian Currie was convinced there was enough promise to lend his support to ensure that the game could hopefully come out in the best possible state as a proper Jagged Alliance worthy title, that the devs have gone on record to say that they don't want to fuck it up because the fans have waited long enough.
If it's not good, I'm going to fucking kill myself, and I don't have a very high bar for acceptance in this genre. All it has to do is not be 7.62 High Calibre.