The moment I read the topic title, the words "Yggdra Union" came into my head. Yggdra Union isn't similar to this in terms of gameplay. Gameplay-wise, I find it similar to Golden Sun and Final Fantasy VI, both of which are awesome GBA games imo.
Muslim The coolest game character imo - http://www.serenesforest.net/story/lloyd.html
Which aspects of Riviera did you like the most? While Riviera is rather unique in terms of overall presentation, there are other games out there with similar elements.
If you like the characters with all their personality, humor, and a touch of flirting, you might want to try the Summon Night Games. These are ARPGs rather than turn based games, but they have wonderful characters and a lot of funny moments. The Summon Night: Swordcraft Story games on the GBA are an interesting fusion of an ARPG with almost a beat 'em up style of battle screen. Summon Night: Twin Age is a great Diablo style, massive swarms of enemies + loot fest on the DS.
If the romance is a big draw for you, you might consider Rune Factory 1 & 2 on the DS. These are a different take on the traditional farming game in that you're exploring dungeons, battling and capturing monsters, and gathering loot, all while still farming as well. And courting your lady fair is a big part of the game. You get to meet all the local gals, butter 'em up with kindness and gifts, and eventually get married and have a child.
"If you master the coolitude, you'll become what everyone calls a hero!" - Arlus, Summon Night: Twin Age
While Yggdra Union and the upcoming Knights in the Nightmare are not similar to Riviera: The Promised Land I would recommend that you should at least look into both of them. All three games are from the same development team in Sting and also are part of a series called Dept. Heaven.
I just finished this game and thought it was a fantastic breath of fresh air, I'm kinda looking for something that keeps focus on strategic combat but I actually thought the very linear way the game approaches exploration and focuses on event sequences was perhaps my favorite part, I can't think of any other rpg thats really done it in even a similar fashion but if anyone has recommendations on that part please tell me :)