Grinding for EXP, and randoim 'world' encounters, very annoying. Leveling up, and creating a unique charachter, very fun. Infinite monsters, very annoying. Tough mosnters that take skill to beat, very fun.
I don't play a lot of RPG's...

Unless you count the nes and snes dragonquest games, nothing can kill an RPG game more than fighting for 4 hours just to gain 2 or 3 levels...

well, there was no level-upping in FF2, but players have to hurt their own characters and cast expensive spells for hours to raise max HPs and MPs..:(((
I'm thinking about a way to dump that, something with story-advancemnt's reards or somthing...

On the matter of charachter advancement. The best systems I've seen so far for advancing charachters were (in order) Deus Ex, System Shock 2, and World of Warcraft. What made it a lot of fun to advance your charachter in those games was two things:

1) EXP found in the world, not the mosters
In all the above games, the best (in the first two cases the only) way to advance your character is to explore the world, and complete quests. Killing a random creature will gain you zero (or a pittance) of EXP, but you can find real charachter advancement rewards by uncovering hidden areas, or completing a difficult challenge. Grinding is eliminated, and this is made even more fun if the challenges can be tackled in a number of ways which brings me to:

2) Mutually exclusive upgrade paths
In order to have the player REALLY personalize their charachter, they need to be able to choose from multiple diferrent, equally viable but absolutley incompatible upgrade paths. In Deus Ex you could upgrade your body's systems in one of two ways. Do you want super strength or fast melee attacks? Fast running or silent running? Night vision or sonar? And so on and so forth.
System Shock 2 gave you three characher templates to start from, a way to choose your initial ability scores, and then gave you free reign to upgrade yourself. But of course there's just not enough upgrade points in the entire game to max out your hacking AND your heavy weapons, for example.
World of Warcraft gives each of its 9 classes 3 seperate "trees" into which to put your upgrade points...making it relateively rare that you'll see two players with the same class AND talent spec. Is he a protection warrior or a fury warrior? Feral or Restoration or Balance druid? etc.
Letting the player put their own "stamp" on the charachter's progress really enhances the player's involvement in the world and adds a lot of fun to the game.

I loved old Grandia for playstation wherre the monsters were present on the map in finite number ad could be avoided with some dodging too... If you like na:f plot-lines (like "A damse in distress? Yays, let's go, i lov to be vored!":) then try it!-) And characters' advancmnt was very intereting too, though not very complex. Bosses were lame, there thoo, in the worse of PS' traditions...
What are you fav monsters?

Well "large monsters that take skill to beat" is more of an action game thing than an RPG game thing. In an RPg if you don't win then you're probably just not high enough level.
But here's an idea: Rather than the typical FF approach to combat, where both sides just stand there and make little numbers appear over each other, perhaps make combat a turn-based tactical affair, so that victory depends at least as much on player skill as on charachter stats.

Mostly japanese semi lineal RPs, I do hate those fps american RPGs and ALL the SNES Ultima games; one thing is enjoying a non lineal RP and another one is a lineal game with no hints whatsoever.

"SNES Ultima"? I'm familiar only with the Origin's / Lord British's ones and they are paragons for me... But i ate the later kind too!

yep, the ultima games simply don't give you a hint whatsoever and you end up wandering for days even just because you forgot one word...