I just discovered a game I must buy for my PSP. Puzzle Quest is a combination of RPG and puzzle game, and instantly addictive. How do I know that? I played the demo, which is available for the PC. Which is insofar strange as the game itself is only available on the PSP and DS, and not on the PC. But even if you don't have a handheld console, I recommed you download the demo and play it to the level cap of 7, because it is so much fun.
The principle of the game is simple. You have a character walking between points on a map, picking up quest. The quests lead to fights. And fights are handled with a Bejewelled-like puzzle game, where you need to switch tiles on a board to get 3 or more of the same type in a row. Just that in this case the tiles deal damage to the enemy, or give you mana of a specific color, or experience points, or gold. The mana you can use to cast spells, of which you gain more as you level up. Winning the puzzles isn't always easy, but you can't really lose. If an opponent beats you, you still get all the gold and experience tiles you collected and just have to start over the fight. Worst case scenario is fighting the mob so long you level up or gain the money for better equipment, and then you win. Besides that you can build up a castle, listen to rumors, buy and sell equipment, and do other typical RPG stuff. It's all in 2D, so it runs easily on a handheld, but the graphics are nice enough.
Of course I immediately started to think about a Puzzle Quest Online MMORPG version, although I doubt anyone will ever produce it. I really liked Puzzle Pirates, but Puzzle Pirates didn't let you level up and develop your character. Doing puzzles as a RPG combat would be a nice change from the autoattack-plus-special-attacks standard fare of MMORPGs, or the click-to-kill versions that are being developed. Puzzle games like Bejewelled have even more players than World of Warcraft, and tapping into these players and offering them both puzzles and a persistant online world with chat and character development could be really great.