Target: Arnhem is an interesting little game, although some who have played it more than I have suggest it has some balance issues.
The larger problem facing Target: Arnhem and other games on the topic is something I'll call "scriptedness," for lack of a better term.
It's a pretty common problem in wargames, actually, and perhaps inherently so.
"Scriptedness" occurs when a game follows certain well-trodden paths regardless of player decisions. An example is chess openings, in which some clearly defined opening lines tend to dominate play and many potential openings are never used by anyone other than novices. The creative aspects emerge in the middle game as players depart from the openings.
In wargames the openings and even middle and end games can be much more explicitly seen as scripted. Sometimes the rules explicitly require certain activities. It's very common for there to be defined setups and often events such as weather and reinforcement occurs on a set schedule. Usually this straight jacket is defended on historical grounds, although this is also the source of the dilemma.
The actual, historical participants, of course, were unaware of any "script" for their campaign. The impenetrable fog of the future meant they were unaware of the proper lines of play. The fog of war meant they had no way of knowing the enemy OB or reinforcement schedule. Indeed, details of their own OB and reinforcements were often lacking.
A more "realistic" portrayal of the action might give players many options to choose from. The problem here, of course, is that players have the benefit of hindsight and a design would have to include many events that didn't occur and possible paths not taken in order to capture the environment faced by the actual participants.
The rub is player acceptance. A game that departs too dramatically from the historical "script," especially in a well-known battle such as Arnhem, will probably be criticized as unrealistic.
And it very well might be, unless the designer goes to great lengths to depict the reasons why certain decisions were made. For example, in the Arnhem operation, given a choice, player might opt to use one of the American airborne divisions for the Arnhem bridge drop and would probably make sure that drop, of all of them, gets sufficient airlift to be completed in one day.
But there were good political and operational reasons for the historical drop plan and those need to be reflected if any change is allowed. And, of course, the Allies were ignorant of the deployment of the SS units near Arnhem, while the player is not.
Target: Arnhem has a defined set-up for the German forces, but gives the Allies the choice on where to drop their units, although when they are dropped follows the historical schedule. Because it's a simple game, there are no rules that might reflect the nuances behind the historical choices, so it's an open question whether giving the Allies this much choice is appropriate.
It does make Target: Arnhem a bit less scripted than many other games on the topic, although it's still very scripted by most other standards.
Unless players are willing to be more open-minded about the potential lines history could follow, "scriptedness" is likely to continue being a common characteristic in wargames, especially wargames about Market-Garden.