This is a fairly large review.  I took advantage of the July free shipping to purchase the 7939 Cargo Train along with the complimentary sets 7936 Level Crossing, 3221 LEGO City Truck, 3180 Octan Tank Truck, and 3177 Small Car.

As I mentioned in the review of the 7938 Passenger train I hypothesized that the cargo train would be a better play value.  Now that I have the cargo train I can say definitively that I think that is true although I do think the passenger train is a fair value.  The cargo train comes with more track then I remember any 9 Volt train ever having.  With 2 Switches, 16 Curves, 4 Straights, and 16 flex tracks there are a lot of possibilities with the track.  Having 2 switches greatly improves the play value.

I will break the train down into the different parts.

1. Engine:  The engine is definitely European but it is a nice set and there is a lot more room for the electronics then the Passenger Train.  Some have had problems with the IR receiver being to low in the engine.  I had no problem but I only used the train inside a small room where the signal has lots of opportunity to bounce.  In a wide open space this may be a problem.  Finally I have to say the "dummy" motor truck LEGO has come up with is the best I have seen them do.  I am sure this is thanks to the new motors that use axles and new wheels but I finally have a LEGO dummy truck I like.
2. Octan Tank Car:  This is a fairly simple build but by far the best looking tank car LEGO has ever done.
3. Car Carrier:  This car is very simple to build and is in no way prototypical the cars are nearly identical to 3177 Small Car.  While not prototypical the car is a lot of fun to load and unload and watch go around the track.
4. Container Car:  Again this is a little less than prototypical but some of the building techniques on the car are really neat.  The container is simple but LEGO had definitely moved to a bigger container.  This is huge compared to the old style containers.
5. Semi Truck:  The cab of the truck is very similar to that in 3180 Tank Truck although it doesn't have mirrors.  The trailer is simple and will work with the cab to 3180 but will not work with 3221 LEGO City Truck.  This is because the trailer uses a fixed axle to hook up and won't allow the trailer to turn if hooked up to 3221.  The container is half the size of the container that comes with the Container Car.
6. Crane:  The crane is fairly simple but nice.  Nothing special but adds significantly to the play value of the set.

I would not say that this set was a difficult build.  While a large set the separately bagged "parts" make this more like 6 small to medium sized sets then one rather large set.  This is a great starter set for someone just getting into trains and the Power Functions parts and motor seem to perform much more closely to what we had come to expect with 9V trains.  I would recommend the rechargeable battery though if your train gets lots of use or if someone in your family likes to turn it on and walk away. 

Click "Read More" below for a quick breakdown of the other sets.

7936 Level Crossing

The vehicle is quite cool although I have yet to warm to the click hinge arms on backhoes and diggers.  The crossing is what it is but getting 4 pieces of track is nice.

3221 LEGO City Truck

This is a great looking truck.  The cab is a fun build and all the little LEGO sets are very cool.  The trailer is a fairly simple build.  The only negative I might have for this set is the angle bar used to hitch the trailer could have been done differently.  The bar tends to "stick" in the hole on the 2x2 round on the cab and usually the 2x2 round separates from the cab instead of the bar just pulling out.  (More on trailer connections later).

3180 Octan Tank Truck

Another great truck at a fantastic price.  $20 for this set is fantastic as it comes with 222 parts, far exceeding the $.10 per part threshold.  Compared to the LEGO City Truck I would say the Tank Trailer is a bit undersized but still one of the best semi-trucks LEGO has done.  Sure an Oil Truck might not be the best choice considering current events but remember Octan has never had an oil spill in its history.

3177 Small Car

Not much to say.  It is like the cars in the Cargo Train.  I will say you have to finagle the driver in to snap the roof back on.  This is probably more difficult to do than it should be.

Rap up on Semi-Trucks and Trailers. 

In all I have 3 2010 Semi's all listed here.  It is obvious LEGO tried some standardization but it didn't work 100%.  The connections between the trailers are very similar but all different.  The 3180 and 3221 trailers work on all 3 cabs but the trailer in the cargo train does not work with the 3221 cab.  A little closer attention to those kinds of details would be nice.  Folks like to mix and match their cabs and trailers, especially kids.