Defenders of Ardania (DA) can be summarized as a tower defense / offense game set in the universe of Majesty game series. As such, it can get a bit frantic, esp. when you add in spells and possibly multiple factions.
You defend your castle with towers, with the restriction that you are limited to 10/15/20 towers TOTAL, and each tower must be within 4 "squares" of at least one other tower (your first tower must be within 4 squares of your castle), subject to restrictions on the playing field (such as you must leave at least one path and so on). Some squares like mine, hill, and power, provides bonuses like extra income, better visibility, and more attack power. Some maps may provide additional bonus tricks.
You attack your enemies by building units, from common guardsman (swarm) and rogue (very fast but weak), to much tougher but slower units like swordsman, mages, and priests. Later you also get flying units and super-tank units. They emerge from your castle and attack enemy castle. If there are more than one, you can choose which one to attack. If they make it into the enemy castle, appropriate amount of life is deducted from that castle. The objective is, of course, reduce the other castle(s) to zero, which also destroys all his units and towers.
The resources you use, gold, is generated automatically, and you can spend them on towers, units, or buy some improvements for the economy like make all units 20% cheaper, make all towers 20% cheaper, and so on. Finally, there are some "spells" which lets you heal your castle (a little) or a spell such as a huge lightning bolt that strikes down an enemy tower.
The main problem with this game is the interface. You'd think the logical way to build those units (and there aren't that many of them) would be to leave some onscreen buttons, but no. The only controls are a pop-up "remote" where you click on one of four buttons (or cancel), which takes you to upgrades (for economy), units, spells, and attack target.
Towers are your typical shooter, artillery, slow, and later, energy. flame, sniper, and so on. There's a twist in that some advanced units CAN attack towers, and if one was knocked down, nearby units will change to shortest route if the tower's destruction opens up a new path.
Graphics are quite decent and has no problem going all the way up to 1680x1050 on my dual monitor setup. Sound is nothing special.
The campaign is a series of "missions" where the new King of Ardania must gather his closest allies and sail forth and solve the mystery of the rising tide of undead. There are also limited resource mode and survival mode if you need more of a challenge.
All in all, DA is a bit of also-ran in the RTS / Tower offense-defense game. As I found Tower Wars to be better, DA with its bad UI issues just doesn't have much going for it other than the name and a bit of shared universe. While the game does offer some unique challenges, the overall effect is a bit of "meh". It's playable, and it BARELY makes me want to recommend it... just barely.
UPDATE: Got to next to last mission, and all of a sudden the game dead-ended for me. You are up against THREE enemies, and once you destroy ONE enemy fort, that fort spawns a superchampion that will ANNIHILATE your fort... unless you can destroy it in time. The problem is you don't have enough room, and the only tower that seem to damage it is the ray (sniper) tower. According to the walkthrus I read, the only way to solve this is setup a stupid exploit... You setup two ray towers in his path, then you build and unbuild towers IN his path to force it back and forth, back and forth, past the two towers until it dies. WTF?!
That's just stupid.