I have been playing GemCraft: Chasing Shadows, a tower defense game. A great thing about the game is the ability to fine tune your difficulty. You can unlock three levels of difficulty. You can unlock nine different “battle traits” that add enemy traits and waves. You can select talisman fragments that give xp instead of bonuses that help you in the fight. During the round, you can on a per-wave basis choose to “enrage” enemy waves, spending mana/gems to boost monsters, and you can spend many small gems for high numbers of enemies or a few larger gems for bigger enemy boosts (or both). Rewards scale accordingly; I went back to an early map with some difficulty sliders turned up and got a score 20,000 times as high. Oh, and then there are achievements for other self-imposed difficulties, usually not using part of your arsenal or doing something very quickly on a particular map.
The base difficulty of the game is fairly low, at least in the paid version. (The paid version is easier than the flash version without the “magician’s pouch” mainly because it unlocks “endurance mode,” continuing the map after beating it to keep racking up xp. Xp in GC:CS is your highest score on the map, so going back and getting a few levels with your new skills and difficulty sliders makes everything else easier.) With many ways to tune the difficulty, you can dial it up to exactly the sort you want. Just want to run through the game and see everything? Keep it at the minimum. Like fighting big targets? Dial up “Giant Domination.” You prefer crushing swarms of foes? You can enrage swarmling waves into the hundreds. Hardcore elite gamer? Turn all the dials all the way up and go for it.
Oh, and there is “Iron Wizard Mode,” which eliminates most of your ability to level grind away the difficulty. Steam says that less than 1% of players have beaten that.
Steam also says that 13.6% of players do not have the “kill a monster” achievement. I like Steam games to have that “have you even played?” achievement. It’s informative.