I love the concept. I enjoy recruiting armies. I enjoy the fact that you don't have access to the best weapons early. Policy decisions, the economy (though it needs a lot of balancing), etc. I like all of that very much.
But my favorite Civil War game is the original AACW with the Struggle for a Vast Future 2.0 mod. It's quite good, and though the AI could use some work, it's very playable. Especially if you play against yourself!
I guess what turns many on to Grant Tactician is the fact that it has a campaign mode and a battle mode. It's the opposite for me. If I'm the President, I can't very well show up in Tennessee AND Virginia in the same week to command two battles. That's unrealistic, so I always use the "autoresolve" feature which I don't think it's fully functioning properly yet. I don't have any comments on the tactical engines because I've never played it.
The campaign AI needs a LOT of work as you might imagine. They made the leader system more complicated than it should be, and without going into too much detail, you seem to continually get stuck with no-names commanding AI armies while guys like Halleck and Lee are commanding brigades and artillery batteries.
Recently as the Union I fought what was basically the battle of Manassas first and second, in the span of a couple of weeks. I won the first, and then the South attacked again with another army. The AI will build a large number of smaller armies and keep hammering you with them. I eventually lost one of the autoresolved battles, and instead of my army retreating to DC, it retreated south to Fredericksburg! There are no regions or hexes in the game, so no zones of control, so armies kind of retreat anywhere they want.
They've done a great job with the game, especially considering it's a one-man crew. Their old game, the Seven Years War, was also a great concept, but it was abandoned a bit early as he decided to focus on the Civil War game. But it needs a TON of balancing and AI improvements.
My take is that the more "stuff" you add to the game, the more features you add, the more types of units, the more leaders, the more options, etc., the harder it is on the AI. This game has a lot of stuff like that, and personally I don't see them ever getting the campaign AI up to snuff to satisfy me. I say that as a long-time player of AGEOD games.
That said, I like the concept of it so much that I keep going back and trying a new game with each patch...only to get frustrated by the end of the summer of 1861 each and every time and ending the save. I hope they can eventually get the AI good enough, because if they do it will be an epic game. But right now it needs a lot of work, and considering there is so much "stuff" that the AI has to do in the game, it will be difficult. Hopefully some skilled modders start working with that part of it.