I'd say every red deck needs the Highlander in it. A second turn 4/4 creature? The first time you attack with it, it'll pay for itself. Same thing with the Knight, but it's two color. With the Goblin, you lose 5 life, but it has haste, so it's a first turn 3/3 attacking critter, so it'll be in any red deck, and certainly in every goblin deck. Soldiers is 3 cost and two color, so it's not as useful. After Chaos is too expensive for what it does, especially since it helps your opponent as well, but it is a cool effect. I like the Rage Elemental for the end of game effect, but I'd switch it to Shroud so you can't just kill it if it you don't win the game in combat. Hunger Incarnation is another cool critter that can get nasty with some decks; it doesn't have trample though, so no matter how big it gets it just takes a caribou, thrull, spore, elf, goblin, etc. to stop it. High Efficiency is brutal in a deck made to exploit it, since most people choose their creatures for the abilities and not necessarily for their power/toughness.
Anyway, for the most part I don't think the cards are overpowered, but some would be useful in many decks, and most would be useful in some way or another. The high cost theme is also pretty original, in my opinion at least.