Operation: Anchorage offers a great, but brief, campaign, and is overall a decent addition to Fallout 3.
Upon having OA downloaded a distress signal will appear, and as soon as you step foot outside the Outcasts' base, the missions begin. This is the only part that isn't the simulation, but after knowing why you must "play" through this simulator, the campaign truly begins.
The story is rather interesting, and the fact that what is being played is really a historic war in the Fallout universe is really cool. The main setting is actually in Anchorage, Alaska, some short time before the bombs fell. The Communist Chinese have invaded Alaska, so it is all out war in this territory as U.S. forces are trying to regain control. It is told that this was a terrible war that suffered huge losses. So what is being played is a simulation that actually prepared soldiers for what they were going to face. And the point of this being played by you is because you have a Pip Boy which will somehow unlock a safe full of supplies that the Outcast are dying to get into.
Anchorage, Alaska looks quite well. It is very mountainous, and the sound effects are great. It's a good break from being in the wasteland all the time.
The gameplay is very similar to that of a shooter. You are faced with a few options, mainly focusing on how to approach and kill the Chinese. There's the silent ninja strategy, the sharp-shooting sniper, or the all out guns-blazing-going-rambo-on-everyone strategy. Supplies and health are replenished from despensors scattered throughout. This meens no picking stuff off from dead soldiers (which actually disappear when eliminated). The story and gameplay is obviously linear, as it is basically a shooter campaign with objectives such as blowing up important military devices of the enemy, taking over enemy bases, and so on. But because this is Fallout, the gameplay overall is a much different pace then what would be experience in a shooter. Depending on how high of a level your character is and what perks you have, this simulation can be very easy to a bit of a challenge, but overall there isn't much that should give you trouble. There are a few different enemy types, one of which are invisible snipers who are only vulnerable when being shot (not in VATS, as it shows as 0% when they are invisible). There is plenty of action and some intense firefights, but again not many choices to make.
Another good thing to note are the few new weapons and goodies that can be use in this add-on. And what's also nice is that you are able to obtain many of these cool new weapons and accessories after completing Operation: Anchorage. The Gauss Rifle especially is a very fun weapon to use, and you don't really have to worry about overusing your weapons in OA, so it's good fun to snipe and shoot almost as much as you damn well please.
Overall Operation: Anchorage is fun add-on to Fallout 3 that adds some decent value, and a decent amount of goodies. However it is extremely short from start to finish, it didn't even take me 4 hours, and I typically play through games slower than other people. Another downer is that once it's over... it's over. No going back to the simulator or anything. The only thing to remember it by would be the cool items you can collect after finishing it, and maybe even a a perk or 2 depening on if you bothered collecting all the intel. I also ran into significant lag playing from the Game of the Year edition. Also the linear gameplay and the short lasting appeal may not appeal to everyone. But thanks to an excellent story line, unique setting, and a good amount of action, the playthrough was worth it.
$10 may seem like a lot for this add-on due to its short length, so it may not even be quite worth the purchase if you're looking for something that will last you longer, or if you want to purchase a limited number of add-ons. However if you have the GOTY edition, it is definitely worth the playthrough.