Wallace explicitly denies any simulation intent, but I think he may be too modest, as it's at least as reasonable facsimile of the battle as many games with pretensions of simulation authenticity.
What Wallace's Gettysburg doesn't have is a strict adherence to scale in either units, geography or time. Units are not measured in or called "brigades" for example, although the pieces typically seem to represent 1-2 brigades of infantry for example. Likewise the turns are not measured in "hours," although each cycle of player acts seems to depict something akin to a half hour's worth of action.
In perhaps the most controversial aspect of the game's presentation, the military units are represented with "meeple" style wooden figures vaguely shaped like marching infantrymen, kneeling cavalry troops and cannons. The CSA side is the traditional gray, except for elite infantry which is in black. The Union side is a little more varied, with blue for the regular infantry and artillery, a darker blue for cavalry, one bright red unit for the elite "Iron Brigade" and orange for the lesser quality troops of XIth Corps.
In a very "euro" style touch, casualties are marked with color coded tiny wooden cubes that match the color of the wounded infantry or cavalry unit and there are additional wooden pieces in a variety of shapes for other game functions.
Among those are some larger blocks numbered 2 through 5 in sets of eight in blue and in gray and corresponding gray and blue discs that are used to mark orders (along with some black discs for Union forced passes), These represent the heart of the game system, depicting the command and control problems of a civil war army in a paperless way.
The basic outline of a player's turn is as follows: Placing an available block (numbered 2, 3, 4 or 5) and then placing an order disc with a block, not exceeding the number on that block. (And not necessarily the block just placed.) That disc entitles the player to activate units in the same area as the block, or sometimes adjacent areas and do things with them. After the activity is done, the player can pick up a previously placed block -- and any discs that it has and return them to his stock.
The most common activity is to move one or two units into an adjacent area (up to four of there's a road). If the area is enemy occupied the move is an "assault" which is comprised of a number of steps involving fire and morale checks by both sides. Losses are marked with the various color-coded blocks and if a unit accumulates a sufficient number of those blocks (usually six) it is removed from the board.
There are other activities such as firing artillery at long range, removing disruption markers and other activities.
A period ends when the Union player has exhausted all his discs in a time period. Various housekeeping activities ensure and the stock of order discs is replenished for the next period. Note that discs remain on the board until their associated block is picked up, so there's an important resource-management aspect tot he game system, in another common euro-game touch.
Reinforcements arrive by a set, historical schedule. The burden of attack is on the Confederate side, but they also have more discs. Victory is assessed at the end of each day, with the CSA winning if he controls two "starred" areas marked on the board that roughly correspond to the historical Union "Fishhook" position. The CSA can also win a sort of "sudden death" victory by occupying the Little Round Top area at the end of any period.
Overall the game manages to reflect the overall course of the battle reasonably well -- it feels like Gettysburg. The pressure is clearly on the CSA to push hard in order to win, but the federals, carefully played, can manage to hold on.
The game mechanics are a refreshing change of pace for wargamers, who won't find a lot of overlap with the traditional hex-and-counter model. It may appeal to non-wargamer euro players who like relatively intricate games. Compared to most wargames it's not very intricate, but it's on the high side for the euros I have seen.
It's definitely playable in a single evening -- possibly even match play suitable for a longish evening -- and until The Guns of Gettysburg came out I'd have considered this my primary Gettysburg game for playing on the battle's anniversary. I think I'll still try to get in a game of it on July 1st - 3rd. There's only one "scenario" -- the entire battle -- and the area depicted is limited to the actual battlefield so it's not much use for exploring what-ifs. But it is a suitable commemoration of the battle and it appears to be scrupulously fair to both players with neither side having an obvious edge. Neither side can afford to be lackadaisical in their play, however, and it should be a tense contest throughout.
Overall I recommend this game as a very nice, entertaining Gettysburg wargame that is more game than simulation but still shouldn't offend the sensibility of the historically inclined.