The graphics and sound work, and to be honest, there is not a lot more to say in that department. Afterall, it is a 2D, top-down, indie release. Humorous cartoon overlays do add to the atmosphere, the user interface is fairly polished, and the sound does fit the gameplay well. That said, the only graphical feature that really stands out is the change of tileset as you zoom out. Nothing revolutionary, but an appreciated feature - particularly in Tower Defense mode.
Dwarfs!? also offers a pure tower defense mode, and for many this is where the game really shines. A single, wave based map is all that is on offer in this mode, but that is all it takes. At the start of each of the first 4 waves, a dwarf will spawn in one of the map's corners and begin digging toward your base. Undirected your dwarf will take the shortest path - not good for defense - and while you do have budget to direct him, you must also leave enough money to purchase defensive towers.
A wide range of upgradable towers, and a great diversity of monsters - from high hitpoint titans, to stealthed units that can only be detected by certain towers - make the tower defense mode satisfyingly challenging; and combined with the fairly unique starting waves, very replayable.
While Dwarfs!? does offer extensive in game tutorials for the exploration modes, I admit that I did have some difficulties picking up the finer points of tower defense mode. These difficulies were the cause of minor frustration, but all things considered, the game is quite polished, and most importantly: I had a blast playing it.

The exploration modes are great casual fun, but for me it is the tower defense mode that really makes the game. With over 17 hours of entertainment provided so far, and with a price tag of only $9.99 on Steam, this game is extremely good value, and well worth checking out.