Dragon Age Origins

Baldur's Gate as has been mentioned is probably the best and biggest RPG around. Play the Enhanced Edition and if you're done with it get Baldur's Gate 2 and Throne of Bhaal (which is basically Baldur's Gate 2.5).

Kingdoms of Amalur: Reckoning, Tales of Vesperia, Tales of Graces f, Suikoden 5, Persona 3, Persona 4, Xenogears, Grandia.

It would be easier to make suggestions if we knew what consoles you own or plan to get.

Big world, deep story, lots of characters?

Classic CRPGs: Planescape: Torment, Vampire the Masquerade: Bloodlines, Arcanum

Console or console style: Chrono Cross, Anachronox, Septerra Core

Hold on for Ni No Kuni.

Big world, deep story, lots of characters?

Well, personal favourite that fits all those is Final Fantasy 8, if you can stomach the graphics today.

witcher 1&2 are great games.

best play it on the pc.

Tales of Symphonia.

- Huge explorable world, check.
- Awesome deep and epic story, check.
- A bunch of cool characters, check.

+ more (dat battle system, dat voice acting). I couldn't ask for more in a JRPG. I wish there was more like it :(

It's on PS2 and GCN.

Planescape Torment
Fallout 1, 2 and New Vegas

Oh yeah The witcher 1 & 2 are amazing if you havent played those.

Xenogears for the PS1, fits all your criteria perfectly.