What a great read. In fact, I'm kind of dumbfounded. I posted a text about 3D on the exact same day this thread was created (except it's in Portuguese), but then I'm now finding out about a much better and more complete text. That's funny to see. Well, I guess I'll just give my two cents (most of it will be redundant). Spoiler EDIT: Just one comment. Couldn't disagree more. Loops and corkscrews are two of the most interesting level design elements in Sonic. They are not there just for flavour, they have actual uses. Loops not only can tease a player with itms on top of them, they also make sure you have a certain speed at the beginning and at the end. That's why they can, under certain circumstances, be obstacles. Corkscrews are the only instance of phasing ground Sonic probaly has. If you stop or don't have enough speed, you fall to the lower ground. If you are coming from the direct path behind it, you continue at it, but if you come from above, you fall. Sure, these functions may not be easily replicated in a 3D environment, but don't ever disconsider them. I would also like to disagree with this: This is not a rule. "Difficulty" and "rythym" are concepts that belong more to the player than to level design because they are a matter of perception. Moreover, if the path the level tries to drag you to (at least with gravity) is the least punitive one, you are not stimulating the player to develop his skills. The actual rule, if there is one, is that there should be enough room (not paths. Paths are also something the player draws within a level) for a player to have his will challenged, be it by positive factors, such as items, or negative, such as spikes - so that the player is forced to develop skills in order to continue. The player must fight the environment and danger can't depend simply on the player's desires. Nearly every Sonic level does this, but the most notable examples are in Sonic CD. Collision Chaos' bottom routes (for instance) are the most dangerous ones, but the ones that require the least effort to reach. Spring Yard in Sonic 1 follows the same principle. That said... could it be orientation is harder to give in 3D because the controls, specifically the analog stick, no longer describes your movement towards the screen edges? If the camera was fixed towards the goal and all the movement revolved said goal, the analog stick wouldn't describe the direction of your movement anymore, but would indeed say how you are moving in relation with the objective. Sonic Lost World doesn't do MUCH different from that, it seems. But I'd like to see stages being built within a frame of a flat cone. The controls might be awkward, but we'd have our orientation.