Some thoughts about the economics (and ethics) of games:
* if a game isn't fun (to me), I shouldn't have to pay for it
* if a game is fun, I should pay for it
* generally, "better" games deserve more money (non-linear)
* ... but I'm skeptical that $500 is ever the right price (e.g. for every LoL champ)
* "time spent playing" is a half-assed proxy for "better"...
* ... but not if you rig your game mechanics around this proxy metric
* pay-to-win games are "bad" (personal subjective perspective)
* if I don't have to pay for a game, I probably won't (sorry!)
* if I'm paying per-month for the game, I feel artificial pressure to play it...
* ... and if I stop playing, I'll cancel
* ... so I can't casually pick it up 3 months later
* ... and I think maybe most people have a limited monthly-subscription budget
* games that have free options have better word-of-mouth marketing
And a few observations derived from these:
* gotta have a demo
* the demo needs to demonstrate the actual gameplay
* getting demo-length right is really hard
* if you have the infrastructure to charge $2/month, you've got options
With all that in mind, here's what I would do (hopefully will do, one day):
* lots of gameplay should be free
* where it makes sense, put roadblocks that players will hit after a while
* .... and then some more after some more while
* charge say $5 to get past each roadblock
* have say 5 total roadblocks
* to assuage cheapskates (5-years-ago me!), give alternatives to paying real money
* maybe crazy grinding?
* even better would be if you could find a way to give players credit-towards-roadblocks if they are helpful to the game community, or to game development
Be up-front about all of this: "Early parts of the game are free! To feed my family I'll be charging progressively for access to the later parts of the game, but I'll never charge a given player more than $25" (or some other promise you are willing to keep)
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By the way, $20 is a lot for an indie game, especially up-front. The humblebundle this week includes ELEVEN games, including several great ones, and the "average price" (unlocks all 11 games) is around $6. So no, I will not pay $20 for your game, are you crazy? Instead I'll go buy the humblebundle for $10, give half of that to charity so I feel like a social justice crusader, throw away 54% of the games in the bundle, and STILL have dozens of hours of gameplay, and $10 in my pocket for the next humblebundle.
Yes, I'm a cheapskate. But this is the reality of the market at work. I'm not saying your game isn't "worth" $20. I bet your game is more fun than a movie-plus-snacks, and people pay $20 for that, right? But your game will be compared to games selling for $10 or less.
Man, I just realized I sound like I'm trying to talk you out of a career in game-dev, and that's not what I want (as a gamer).
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One more thought:
You said "(not necessarily more powerful, but rather more diverse)". Yeah, listen, when you play my Rock Paper Scissors online game, you get Rock for free, and pay for Paper and Scissors. They're not necessarily more powerful, just more diverse.