mEmO: idea of having every spell have it's own experience so as you use a spell it levels up all spell but at a slower rate of the spell being used and Richard Phipps idea of using stamina bars to get the play switch there attacks both of theses ideas would work well together you have to remember there is a 1st best and a 2nd best spell alway when fighting monsters
you don't beat all the monster with you most powerful spell or the most effective spell

Warnings and advice, sure. In the beginning of the game, this is absolutely necessary.
Making the game easy is not necessary. Easy games suck.. and I don't think I'm the only one with that opinion. After about 5 hours of game progression, there should be very few warnings. The player needs to be kept on his feet, not sitting there expecting what's next.

In my example way above ("There's a fire cavern ahread!"), that would not be necessary later in the game. The player should expect elemental monsters, and should have a good grasp of what elements are in the game and their weaknesses at this point.

Being hand fed is too easy for the player, and will lead to a boring cinematic RPG and nothing more. If the only decisions the player makes are his class, his hair color, and which direction he should turn at the next junction, it's not a fun game. You haven't said what is fun, to be honest, which is what we're trying to accomplish in this thread.

I think I'd rather judge for myself. Being a player and all. Personally, I find character advancement the most fun when I'm the one making the choices. That is, afterall, what character customization is all about.
Not that other methods besides actually using the skills you gain can't be fun, but I enjoy it.

No offence X-G, but you haven't given any type of solution, additional idea, or anything. Just a bunch of negative comments. If you continue, I'm going to have to call you negative nancy from now on.
So, what ability system would be fun, X-G?

Seems like you two are going to have your own little elemental battle to me! Make sure you have plenty of tonics!

Ok, Nancy

This is one very small element of game design. All you've done is shown flaws in other remotely related ideas. For example, elements was not a part of the initial idea. Who knows if they exist in the game in which this idea is placed into? Whereas elements seem to be your primary 'problem'.

It's hardly forcing him to choose every element imaginable; assuming elements exist. Two elements would be perfectly fine if monsters only had one resistance. If not, then the player might need one more.
Some areas will simply be more difficult than others, and that's not a problem. Choosing many elements will just create a balance in difficulty from area to area. It'll be clear to the player that this is the best choice, like in any other game.
Choosing one element will make certain areas very near to impossible, but in my opinion that's how it should be. It's up to the player which he chooses. If he wants to play with 4 white wizards in Final Fantasy, he can. If he wants to bring fire as his primary attack in the fire cavern, he should be able to do that too. I'm not saying it's going to be easy, or intelligent.. but the option is open to him.

Who knows though. Maybe he also selected his race as a lizard, so he's weak against ice and resistant against fire. In which case, he has little reason to practice his ice spell - fire enemies shouldn't be a problem anyways.

If you really wanted to allow the player to use only one element, a spell could be added that would change the target and remove all weakness/resistance. For example, Polymorphism. It's going to drain a lot of mana, but the option is there, and would be a decent strategy.

You haven't mentioned many real flaws, in my opinion. Just that the player is going to dislike casting the same spell over and over again, just to find out it's not going to work on the monsters of that element. To that, I say duh.

There's many solutions that would allow that, but I wouldn't recommend actually using any of them. The player just shouldn't do that, or want to do that. Who does that, anyway?
One solution is completely non-linear game play. Don't want to go to fire areas? Then don't. Clearly if all you have is fire, it's not a place you'd want to be anyways. It's restrictive to the player in the sense that he can't get things from the fire cavern if he doesn't go there, but in my opinion that's not an issue, because he chose not to.

I know, you're not even trying.
If you ask me, you're not thinking your problems all the way through. If you did, you'd find some solutions.

Derezo hits X-G with Logical Melee for 16 hp damage!

X-G attacks Derezo with Evasive Sarcasm for 10 hp damage!

Red X-G is about to die!

I can hardly believe this is still going.

I would agree with Derezo on giving the player choices, I think that every time a game ends it should only be the players fault. If you took your fire spells into your fire cavern only to find out that they heal monsters instead of hurt 'em... well... that's your problem.

I also think that it's fairly simple to craft a solution that merely suggests to a player - hey, you're in town here and the magic guy at the store sells fire spells at half off, and oh yeah... there's this cave and there's nothing but nasty ol' ice creatures in it. What's left is for the player to choose their own demise. If you want to be a moron knucklehead and do the opposite of what people tell you to do, please, do it but do it quickly - we hope to keep the genepool clean of those knuckleheads

Am I missing something? Is there more to this? Should we be talking on the level of ... aha! I just re-read the initial question.

Battle Engine stuff
You should check this site http://www.gamefaqs.com/console/psx/game/24831.html for the FF3 Algorithms. It's really a good basis for trying to understand the different possibilities in a battle engine and suggestions on how to compute 'em.

Flow
A lot of people will tell you linear games are no fun. This can be true but with a well-crafted game
world should not be the case. It requires a lot more work, IMO though.

I would try for a mission based flow. Something along the lines of Final Fantasy Tactics Advance. Have some missions that are story based and the rest help you get to those missions. I'm really considering a mix of the two myself...

Items
Having an inventory is fine. You might want to consider equiping and unequiping items as well

Bottom-line
A lot of this is up to you. You should have a more clearly defined goal of your game before asking really general questions. (As I'm sure you can tell with the 4 pages of posts). If you said I'm thinking of a spell system A over spell system B. Can anyone help me hash out the pros and cons? - that would have worked wonders to stear the thread to what you're really after.

Just my 2c.

One choice is no choice. Like I said, if it is merely a question of "pick the one right, obvious solution," then it isn't very interesting. If it's "use fire spells in the ice cave or die," how is that interesting? Since it is an uninteresting choice, what's the point of having the option at all?

All of these kinds of questions are questions you should answer yourself when you design the game. There's no right answer; it all depends on what kind of game you want to make.

Are you trying to make a Zelda-style adventure game, a Final-Fantasy-alike, or a modern PC-RPG-esque game? Or something else entirely.