Fallout Tactics, the grey sheep of the series: not quite the black sheep of Fallout: Brotherhood of Steel, but it's just a matter of shades. I tried to like this game: I uninstalled it, then reinstalled it twice before ultimately dropping it. I think it remains obscure for a reason.
There is not one big flaw I can point at. It's a cavalcade of minor issues that get in the way of enjoying the game. I can usually brush those aside - I've quite the tolerance for old game awkwardness, but there is just so much of it.
The game runs in real time by default, but without a pause button, it's hard to do any precise work like VATS shots. In truth, everything's running on the same skeleton as the first two Fallout games, and there ARE two turn-based modes... but the game wasn't designed around using those either. It slows everything to a crawl, and on some levels, you'll be sitting for half a minute as unalerted enemies go about their turns... oh, and the UI for figuring out your movement costs is a pain.
Regardless of mode, sightlines are important, more so than in the older games because of the new stance system, but you're getting no preview or display, so you'll just have to guess and hope for the best. And when the fighting is done and it's time to loot? The Fallout inventory system was designed for one hero with maybe some helpers, not squads of up to six. Have fun fighting with the range restrictions when you're trying to transfer gear, and then, once you get back to base, moving all your gear to the one squadmate with Barter so you can get a reasonable amount of scrip for your trouble.
There is so much more. The pathfinding in general is messy, melee sucks, some skills are nigh-useless... It's all too much for the six or so hours I ended up spending on the game. And, yeah, that's the game. It's combat missions strung together by a basic plot. If you don't like that gameplay, you don't have a reason to play, and I didn't, so I won't. Maybe you will?