I'll make this review short due to not wanting to spoil much of the game for those who have not yet played. Most of the game is meant to be trial-and-error so you learn new mechanics and tricks from each play-through and I would rather leave that up to playtime, instead of a simple review.
This game is an absolute classic and is still just as good as ever. I would fully recommend this to anyone who is interested in Turn-Based Strategy, and have played the original X-COM games or older Turn-Based games. This is not for those who don't like difficulty or challenge in their video games, and it sure in Hell isn't for those who don't like older games.
Jagged Alliance Gold is intuitive and has better design and features than 99% of games that are made today. Things like unit exhaustion, explosives turning out to be duds or not going off when they're supposed to, and mercenaries who not only have certain strengths and weaknesses outside of stats, but have their own personalities and will voice their opinion when they feel like. Something as simple as having your band of mercs have their own wants and needs is something that most games two decades later can't achieve with 100x the budget and you really have to ask yourself why that is.
Overall I'd give Jagged Alliance Gold a 10/10. There's a reason why it's considered the Great-Granddaddy of all Turn-Based Strategy, and it still shows even to this day.