Edit: Recently, someone called this "ranty". I'm a pretty ranty kind of guy, but I'm not trying to rant, here. I'm trying to explain using some specific examples, but it doesn't mean I think more or less highly of those examples than others not mentioned.
Last post, Chill made the following innocuous comment: "Meaning that there may be a few stats, but the important thing is that there a lot of places on that scale that one could be... Point is, the more actually different ways one can affect a system and get meaningful feedback, the better."
I think he was trying to agree with me, but this is a chance to spring some fundamental design principles on both of my readers, so that's what I'ma gonna do. Chill's comment provides a useful springboard.
I no longer believe anything I quoted above is correct.
It hasn't been long since I changed my mind, though. Less than a month.
I think that the key to good gameplay is a few simple rules that produce complex results. But... I don't think that's clear enough. Let's give a surprising example:
In a shmup, you have a spaceship. The interaction is simple: you can move, you can shoot, you can use the bomb. Pretty simple? You know what I think when I look at that?
"What's with the bomb special case?"
The bomb isn't a deep rule. It just rescues your ass when you prove to be too inept. It serves the same basic purpose as a life. Why does it exist?
Some shmups have a really nifty bomb. For example, it switches what enemies you're immune to, or it sucks in bullets and turns them into a super-shot. You know what I say then?
"What's with the bomb special case?"
The core of the game is moving and shooting. You already have moving and shooting. If you need to add a bomb mechanic, don't. Change your shooting or moving mechanics to be deeper. Or make something automatic - either the bomb or the shooting - so that it isn't an interaction rule any more. Having duplicate attack mechanics is just saying "our design-fu is too weak to make any of our stuff actually good, so we give you more rules and hope you don't notice."
"Did he just say that shmups are too complicated? Shmups, the simplest game outside of match three?"
Not exactly. I'm saying that shmups have too many ways of meaningfully interacting with the same system. Modulating your movement, shooting, and how you die... if you can't make deep gameplay out of that, you're just screwed as a designer. As a designer, you should be able to make deep gameplay out of any one of those.
There are games with "complex rules". For example, action RPGs. Let's say: combat movement, world map movement, combat moves, items, equipment, money, leveling... tack on optionals like managing team-mates, social management, plot trees, TACOs, skill challenges...
I'm not saying those are bad. The rules in good games are chosen so that they feed each other but don't step on each other. While you can slice with a sword or cast magic fire or throw a grenade, those are actually just one rule: attacking. You modulate the cost and effectiveness of attacking, allowing the player to express himself within the rule.
The problem with phrases like "places on the scale" and "lots of ways to get meaningful feedback" is that they do not actually encourage good rules. They simply encourage rules.
Being at a point on a scale is not a very good way of expressing yourself: it's too one-dimensional. The good news is that in a game like Magic the Gathering, you're not just expressing yourself one-dimensionally. Sure, you show a preference for a particular mana cost, but you also pick a particular color and, hell, particular cards. It's one of the most expressive games out there. While the actual combat has a lot of dumb rules that aren't deep, the actual game of Magic the Gathering lies in creating and using decks of cards... a simple but very expressive set of rules.
Getting meaningful feedback isn't important, either. Again, a rule should allow the game's characters (or other challenges) to express themselves as well. It's not about feedback: it's about establishing a distinct feeling that this part of the game has a personality and something resembling a will.
The rules for combat are relatively simple, but by giving monsters different combat stats and capabilities, the ice caves of Hrraaaalg play very differently from the soldier's barracks...
So don't think of rules as being deep or wide or good or bad. Think of rules as tools for expression, and if you can't think of a way to express a wide range of intents and personalities in the rule, don't put it in.
And, of course, if there's another rule that lets you express yourself in the same way, but not as well, kill it. It's just extra fat.
That would have been a good place to end it, but I have to say this:
Adding more guns isn't adding more rules. It's simply adding another permutation to an existing interaction (in this case, the "attack" interaction). This can be good or bad, but it's an entirely separate question.