So, I've started work on a Geometry Wars clone (as if there aren't enough ) and I know all of the games have some aspect that seperates them, such as the black holes in Geometry Wars, that must be "farmed" for the best possible scores, but not left out of control.

Basically, right now, my engine allows different enemy speeds and characteristics (I have one slow enemy that follows the player, a bullet-like enemy that moves faster, but can not change direction after spawning, and one that is is similar to the following enemy, but is as fast as a bullet-type enemy.) I also have made a spawn system that will randomly spawn an enemy at a random point, at least a certain distance from the player (each enemy has a different distance, such as the slower ones being able to appear closer when they spawn) and the spawn is indicated by a "ring" created by particle effects.

I haven't done work on this in a while, but figure I can use the Geometry Wars clone engine to work on an actual game.

I am looking for something, like the black holes in Geometry Wars, that adds a deeper level of gameplay, along with a twist. Any ideas on what I can use?

Have a look at how the maths behind combat systems (in general) work.

An interesting thing is the interaction between attack speed, enemy number and enemy strength.

If you have a fast attack that only does a small amount of damage. For the sake of discussion you can do 10 attacks each second with each attack doing 10 HP of damage (total 100 points of damage each second).

If you had 10 enemies each with 10Hp, you could destroy them all in 1 second.

But, if you had a powerful attack that did 1 attack each second and does 200 HP damage (for a total of 200 damage per second),

How long would it take you to kill the 10 enemies? It would take you 10 seconds.

So which weapon is better? The slow one that has a DPS twice the value of the other, or the fast firing weapon?

Well, in this case it is actually the weaker weapon. But what if you had an enemy that had 200 HP. In this case the first weapon would take 2 second to kill it, but the second weapon would kill it in 1 second. In this case the second weapon is better.

As you can see, this kind of thing can make your game have more strategic depth: Should you take the first weapon, or the second?

As an exercise for you to think about what if you had a weapon that is half way between them (30 damage each hit with 5 attacks per second). Is this better or worse than either of the other weapons and when would it be better or worse?