The idea is that I don't want a zelda knock off, but instead an MMO fantasy game where the player controls the actions and not the computer in the background. This is a "twitch" based game. Skills determine weapon use/damage, but not hit/miss. Players Dodge Enemies can miss etc. What are the limitations of such a game?

They can't save you any money on car insurance.

It won't get you women either. [lol]

Wait... can you elaborate a bit more on your idea?

MMO means massive, and so you'll likely have a problem with the sheer mass of data being transferred through the connection. A simple FPS doesn't have much data involved. A vector for your motion, a value for what direction you're facing, and what (if anything) you're shooting is about it. Other tidbits like how much health you have can be handled without too much difficulty. Even so, latency is a pain in the butt. A little twitch here or there, and you're dusted. Generally, though, the long-range guns used in the game are pretty random, and unless you're sniping, hit detection can be a little bit squirrely.

Something like OoT would require much more specific data on location, you'd have to be flawless in your handling of distance, position and movement, because melee combat is a lot more delicate than gunfighting. Anyone remember Rune? My head flew off for no reason in that game, and my sword never hit anything. A little bit of lag will end a fight and piss off a player.

That's why PnP rules for combat work so well in an MMO setting. The server fights for you, and occasionally tells you how its going. Real-time hand-to-hand combat is no good online. AvP had this problem, Halo 2 has this problem, although Bungie has a few very elegant tricks that fix it, and any other online game where timing and distance are relevant to victory will have this problem.

Phantasy Star Online Eps. I & II did pretty well, but it was an anemic system, and rather pathetic at the end of the day. Only a few characters could participate at a time, and the world was cut up into tiny little sections. It's hard work, and many concessions must be made.

You could always do monster and NPC battles on the client-side, though you'd have to worry more about people hacking in that case.

That's true. Client-side work would be handy. Really, if you could make as much as possible client-side, and limit player interaction to about the level of an FPS game, then I think it would be alright. It would require a number of concessions, but could be feasible.

anything you do client-side can (and probably will be) abused by cheaters. for example, if your client handles the battles with monsters and then tells the server "this guy killed that thing, give him XP", someone could easily hack the client to say that without even having to fight.

One thing you could do is (provided your not worrying about sensoring chats) make the chat service more peer to peer (the ips of players are provided to the client, with the chat port, and the chatting is handled directly , or in a peer to peer fashon.). You could also use a banking server to handle player transactions and such, that would be more then reasonable and very secure.

im tired, mind the spelling