Is it good? IMO it is a good game.
How does it compare/differe to Fallout 1 and 2? Well Fallout Tactics is a Tactical Squad Based game in which you are given missions from command bunkers. As you complete missions you advance in the story, and expand to new bunkers and new missions. It is not an RPG. There is little in if any RPG mechanics, other then how well you finish the mission and there are four endings. You can have up to five squad mates and you control them as if they were your own character.
How is the writing: I would say it is good. But yeah it is a Tactical game, not an RPG. Combat is pretty much what it is about. Speech is useless.
Steam or GoG in this case shouldn't matter Fallout Tactics doesn't need any patches to run on windows 7, XP and so on as far as I know.
There is a real time option and I would suggest playing using that, it greatly speeds up the game play.
@Gabriel77Dan the super mutants can be very hard to fight, the main point of that mission is to get in and get out, not so much combat. That is why they tell you to not even bother fighting the fort. But given that you know what to expect, why not prepare for it? Have some heavy weapons people, a sniper and a good repair person.