Owners of the original version get a key for free. I got mine already, the Steam version is a big improvment over the standard version. However, it is also a little buggy.
For those who don't know it: Immortal Defense is a very unconventional Tower defense game. It has absolut NOTHING in common with other TD games. Except, well, that you can build towers, which is the main reason why you label a game TD.
But except that, the game tries everything to be not like others. And succeds.
But is it also fun? Different does not mean better. But Immortal Defense is better than most TD games.
ID showed me at te time I played it, that TD games can have a very deep story. Something that very other TD game lacks.
IDs story is one of the best written stories in gaming history (in my opinion of course). It fuses sci-fi elements with spiritual ideas.
The main idea is: If you become an all powerful, omnipotent and immortal being, what would you do with the power? And how do you interact with others?
To sum it up, you play a male person from a planet called "Dukis". Your planet is part in a peaceful but small federation of different systems but someday an alien empire from a far place in space start to attack you and conquer your planets. The Bavakh are a very advanced race that uses genteic engineering to develop biological ships and powerful weapons to destroy everything in their path. You have no hope to defeat them. But another race that comes along the Bavakh as slaves, defect to your side and give you Pathdefense, a new technology to fight the Bavakh. Pathdefense allows a person to abondon their body and ascend into a higher plane, called Pathspace. In Pathspace you can see the Hyperspace routes of the Bavakh as lines and attack them their with nothing that they could do against you. For them you are merely a ghostly presence that attacks out of nothing.
The player takes the place of the defender of Dukis in the hope to protect his home and his pregnant wife from the assault.
One of the main differences in this game to regular TD games is, the player fights with the towers. To be exactly, at the beginning you have no towers, you fight alone. Your cursor represents you, it is your mind and wherever you move it is where you are. If you move it closer to enemies it fire autimatically, no need to click anything. Thay way you are guarented to attack any enemy and miss no one.
Other (AI) Path Defenders might come to your aid and you can see their cursor on your screen. Despite that, the game lacks an actual multiplayer which is sad.
Now you may ask how towers can exist in that heavenly scenario. You are nothing except a mind. You have no building material, no arms to build something. And that's right, there are no real towers. Instead they are called "Points". Those points are manifestations of your own personality. They represent the thoughts and feelings youz have out there. You start with the fear point because fear is what drives you. The fear you could loose everything. Other points will follow and everyone reacts differently.
Fear for an example is a very defensive point. He has a small range and he does little damage but he stuns enemies and can disable their special abilities.If he hits a target multiple times in a row he might even push it back. Courage on the other hand is an offensive point, it represents the overcome of fear after you've learned how to use your abilities. It shoots long range javelins that pierce multiple enemies and every level of the point adds a new javelin to the attack. The shots can even wrap around the screen.
All points behave entirely different and work better on specific enemies.
You can however not freely build your points. Instead you have a set point pool at each level, for an example you could start out with two fear points and one courage point. You cannot build any more than these but you may gain more. You towersgain "achievments" when they attack enemies. When the've reached a specific point (lot of damage, lot of kills) you gain a new point of the specific type.
Money behaves also differently in this game. You still get money when you kill enemies, however you keep all your money on the end of a level and take it to the next one (plus a bonus so it's guarented you have always some money to spend). However, if you've lost any lives during a level you will keep less from your money. Only 50% lives mean 50% money kept. This changes also the way how you play the game. You will save a lot of money towards the end of a level so you have more int he next one.
There are also no waves or anything like this. All levels are survival levels. You have a set timer and an endless amount of enemies appears during this time. When the time runs out you've won. Exception are the boss fights, when you kill the boss you win the level.
I would really tell you more why this game is so awesome but you get the best experience when you literally know NOTHING about it before you play. And I don't want to spoil anything. Trust me, it is a very deep story and the gameplay is also very deep with a lot of surprises.