I have had this set for years, and it has seen much use - mostly in Mordheim and Warhammer Fantasy Battle (sieges).
Most recently I have used it for a siege using the Kings of War rules.
It does the job and does it well.
You have a choice as to whether to have interiors for the buildings or not - I have gone with interiors since I do use them for RPGs on occasion as well.
A friend of mine used his set to create a Gormenghast - a bloody huge thing, no interiors, standing about five feet tall, built in layers, with Christmas presents for the cliffs below.
I have never built anything that... massive. Typically my builds will fit, more or less, into a three or four foot space for the outer walls. (The fellow also used a World Work's ship model to make a ship to wear as a hat on St. Patrick's Day.... Adding a shamrock to the sails. The man is daft....)
The builds are somewhat complex, though several of the more involved bits also have simplified versions. It can be built and used in a modular fashion - each tower, bastion, wall, building, and gate a separate piece. If you do so then I recommend putting it on a fairly solid base - I have tried having them just sit on the table, and they can get chewed up around the bottom.
For most games the castle will dominate the table in a nicely impressive fashion, as a castle should. Properly based the set up is very stable, I have never had a tower or wall fall over.
They are also surprisingly solid - I had a line of metal GW ogres manning the walls and the held up with no troubles.
The gatehouse is the best and most impressive piece.
All told, this is my third favorite World Works set - behind Maiden of the High Seas (my all time favorite piece of PDF terrain) and Cathedrae Noctis (which has seen regular use in Mordheim).
It is not a part of the TLX system - so the pieces do not fit into small neat boxes, but it looks better so... it all depends on your needs.