This game is easily in the top 2 for the launch titles (along with SSF4).
I've never really played many turn-based strategy games and I love this one. Sure there's no voice, but there are some animated parts every once in a while. The 3D is decent, and since it is top-down, you get a good sense of depth.
The play mechanics are solid. I don't feel the computer cheated at all so far, and when you get stuck at certain points, even if you try something different, the computer AI works differently.
The characters get some kinds of personality via the story/text bubbles, and you get to control 6 Ghosts (eventually.... along with non-Ghosts as well).
I'm on Chapter 3 now. The difficulty even on Beginner is ramping-up. There were some *very* hairy maps in Chapter 2. When you get out of the open areas and into caves and bases, you do experience some 'fog-of-war' type stuff... you have no idea what's through a door.
Once you finish a campaign mission, it will usually open-up a Skirmish map, or a co-op map, or another map (sorry forgot the name). For completing the Campaign missions, you will receive between 4-8 stars to distribute to your squad for upgrades.
You may think, 'oh, I get to buy 10 upgrades for every Ghost that's cool', but then when you get a 10th upgrade, another row opens-up and you realize there are probably 25 upgrades to get (I think?)! Besides more health, I've gotten better guns already, and add-ons like Armor.
It says there are 35 maps and 20 skirmish maps total (I have 7), so I am probably less than half-way through so far.
As for difficulty levels, I believe the only difference is the HPs and damage are upped, but someone who's farther along can confirm/deny this.