When people talk about the whole gritty-ness thing, they're complaining how everything looks like it's been giving a fine goating of grit. You only ever see browns and greys, you don't see many other strong colors than those few types of colors. That's a nice thing about Fable and Halo; the color palette varies from levels to level and they contain bright, strong colors to make things interesting. Look at Gears of War or Call of Duty. They look the same. Everything is brown, gray or rusting.
The thing is, they are fucking identical. Enemies in COD or GoW look different from enemy to enemy. Sure, there's only a dozen or so different enemies overall, but with their faces will be slightly different, or they'll be wearing a helmet, or goggles, or something to distinguish them from the other enemies, and not just in the "He has a shotgun, he has a sniper rifle, he has a Lancer" type of thing. When you're fighting dudes in gasmasks and identical black-on-black outfits, it's hard to tell them apart.
Yes, the singleplayer aspect can be a bit lacking, but they're also expecting you to go back and play on hard, and then fuck-you-hard.