Set 5913 is currently available from TRU in the US for $29.99
It's essentially a cut-down version of the 4836 Dragon's Dungeon set, but at $45 less it's obviously aimed at the tighter American pocket.
The Wizard is missing from this set, leaving the other three denizens (two human and one dragon) unchanged.
There is at least some attempt at internal bracing in the box, to prevent scratches and other damage that so often occurs during shipping.
There is a large new baseplate piece that the tower clips to, supported by three separate and different rock formations connected by the usual white clips underneath the baseplate. With just the one layer of supporting rocks the completed tower stands slightly shorter than the 4836 Dungeon, but with the option to connect further rocks underneath.
The doorway is now open, a new moulding for this set I think. There is a nice dragonhead above the door.
The assembled tower has the same rotating catapult on the top, with the same stickers to apply as in the 4836 set. The windowframes and torches are left out, but could easily be added via DS
if they are ever in stock...
Surrounded by the other tower sets and a group of Dragons, the tower certainly fits neatly into the Dragonworld theme.
For $30 I don't think you can go far wrong with this set if you like the Dragonworld theme. It lacks the elaborate bases of the other towers, but substitutes an equally acceptable base which can easily be extended if desired. It is nice to have (at least) three opposing groups in a theme for the various alliances possible, and this tower provides that third faction with a base of operations.