I am of the opinion that the Cube is underrated in the RPG category. Here are my suggestions, for what they're worth:
- Tales of Symphonia is a pretty good "traditional" RPG, with all the leveling-up, item acquisition, and such. It isn't without some flaws, but it's good for 50-60 enjoyable hours (plus decent replay value) and a terrifically addictive action combat system built around a serviceable enough plot. No random battles. Good graphics and voicework. I disagree with the overrated remark, especially now that it can be had on some sites for $20-30 used. Definitely worth it at that price. Some co-op multiplayer, although it's really a single-player game at heart.
- Skies of Arcadia is also a traditional RPG... and it's good for 50 hours for only $20. It's odd because the graphics are dated, the random battles are numerous (although the game alleviates this problem later in the game), and the dialogue is clunky.... BUT, the characters are charming, the plot is endearing (if simple), and the game as a whole really sucks you in. And the music is pretty cool, too. This game is better than it should be.
- Baten Kaitos is also a solid RPG that uses cards in a real-time fashion (think speed poker). It isn't a perfect game (the voice-overs leave something to be desired), but it's really pretty and has a surprisingly-addictive combat system. The plot isn't revolutionary, but it is charming. Good for 60 hours.
- Paper Mario is a little different than the traditional RPG, but it's one of the Cube's best games overall and is good for 40-50 hours. Great plot, nice graphics, hilarious dialogue, cool battle engine. Not really an RPG purist's game, per say, but that doesn't mean it's not a great game... it's a hybrid of Mario and some RPG elements, like Superstar Saga or Super Mario RPG (SNES).
A few others that often go overlooked:
- Gladius: often-overlooked tactical RPG (like Final Fantasy Tactics); pretty good production values, interesting premise, good for 40 hours x 2 different storylines. A little repetitive (arena-style combat) but offers a good amount of variety, too. OK co-op and competitive multiplayer functionality. It can be had for pretty cheap ($10 to $20).
- X-Men Legends: action RPG in the vein of Baldur's Gate: Dark Alliance. Great plot, great characters, OK graphics, nice leveling-up system, decent mulitplayer functionality. 25-30 hours.
- Baldur's Gate: Dark Alliance. It is, unfortunately, an inferior port of the Xbox and PS2 versions, but it is still pretty good (if choppy at times) and can be had on the cheap. 20-30 hours.
- Gauntlet: Dark Legacy. A ho-hum single player but pretty cool multiplayer game. The graphics won't blow you away and the leveling-up system is pretty simple, but it is still a lot of fun. Pretty long, too.
- Lord of the Rings: The Third Age. Traditional turn-based RPG. A little disappointing, but has its virtues. Worth a look if the price ever gets down to $20. 30-35 hours.
- Mega Man X Command Mission: A little short (20-30 hours), traditional turn-based RPG. Pretty game, average voicework. Worth a rental at least.
A couple of other remarks:
- Final Fantasy: Crystal Chronicles is designed around GBA connectivity, and is sort of a disappointment if you don't have multiple GBA's. It is gorgeous, though.
- Lost Kingdoms 2 is a little disappointing, too, but it is worth a rental at least, and others have found it to be more entertaining.
- PSO I and II: I got the "Plus" version and it is probably not where I'd prioritize my money, at least in hindsight.
- Evolution Worlds? Just stay away.