All of the Grax steam locomotives portray famous preserved passenger engines in North America. These engine currently run in excursion service in real life. If you are a fan of those engines then you will want them.
There are drawbacks to this DLC, however. First off, these are older DLC models and are starting to show their age. Their textures look simplistic, fine detail is lacking and there is a distinct lack of functioning animations such as the throttle reach lever, the reach rod and radious rod of the valve gear and windows which don't appear to open when viewed from the outside of the locomotive. Also, while the engines have a lot of smoke emitters to simulate the various steam and smoke exhuasts (a nice touch), they are not animated. For example, the emitters for the injectors, feedwater pumps, and coal stokers/oil lines do not shut off when they should; they are always on. Additionally, the safety valves/pop valves are always on; newer model steam engine DLC feature animated valves that 'pop off' when boiler pressure reaches maximum and shut off again when BP falls.
All of the Gtrax locomotives including the Southern Pacific GS-4, the Nickel Plate Road S-2, and the Spokane, Portland, and Seattle E-1 engine are underpowered; they cannot and will not cruise at track speed with tonnage. They cannot keep up steam the way their real-world "superpower" counterparts do. This severely limits their "fun factor". However, there are free physics upgrades for the Gtrax engines available at Railworks America.com.
The best ones are by a fellow who goes by the name DtrainBNSF1. These mods will improve the handling of the engines to more believable parameters.
Also, there is a problem with the locomotive engineers; on all of the engines the engineers seem to be positioned too low in their seats; this "sinking engineer" problem never should have made it through quality control. Fortunately, there is a third party utilities software package for Train Simulator called Railworks Tools, available at RailworksAmerica.com.
It is donationware and worth it. It will give you the ability to raise the engineers to their proper locations.
Lastly, none of the engines have any 'steam era' routes to run on. They must be run on routes that are set in the modern era, as these are the only routes that we have available to us. This limits their use in scenario creation to those dealing with modern subjects.
Overall, if you want these engines, wait for a sale. If you want a top-quality steam locomotive, save your money for the Union Pacific F.E.F. or the A.T.& N. Consolidation, both from Smokebox, and available as DLC for this game. They are well worth the money and on the opposite end of the quality spectrum from the Gtrax engines.