The DS has many fantastic games, and it is the system for which I own the most RPGs. Narrowing my recommendations down to five was difficult, taking into account what I thought many people would enjoy, not just the ones I loved the most. Each of these games provide a different, but entertaining, RPG experience that I feel would appeal to many RPG fans.
#1 · The World Ends with You
One of the most original games for the system, no other RPG takes advantage of the DS's hardware like it does. The battle system is two at once, which while it has a bit of a steep learning curve, is imaginative and a lot of fun. The story is fantastic, with a creative modern fantasy setting and many great, unforgettable characters. The music encompasses various genres, such as pop, rap, hip-hop and rock which really suit the game world. It also has an incredible amount of replay value, with an extra chapter made available once the main story is done, the ability to earn special reports on a replay to expand upon the story more, and many things to collect such as Pins and Noise Reports. If this game has one failing, it's that it sometimes feels too complex. For the most part, however, I feel that this is a game everyone should try.
#2 · Shin Megami Tensei: Devil Survivor
As someone who is very new to the Megami Tensei franchise, I really got into this game, despite not usually being a fan of dark stories. It is an incredibly engaging plot with some great characters. Not only is it an interesting take on how society would handle an apocalyptic situation, it is also partially a dark parody of monster battler games. The battle system and the means of buying demons on auction and fusing them are both excellent. I found the difficulty refreshing, though others may find it frustrating. True, an enhanced 3DS version will be out soon, but if you don't have the system and won't be getting one for some time, then the original is still worth a play-through.
#3 · Pokémon Black/White
The latest games in the Pokémon series, and in my opinion the best so far. While the controls have sort of taken a step backwards compared to HeartGold and SoulSilver, nearly everything else is excellent. It's the most story driven main series Pokémon game yet, with some very interesting characters. The Pokémon themselves are some of the most fantastic-looking and creative creatures yet in the series (though some of them are perhaps TOO creative). All of the game mechanics are there, and being able to use TMs over and over is very welcome. Even the music is excellent, and arguably the best in the series. Even if you've been out of the Pokémon loop for a while, these games are still worth checking out.
#4 · Phantasy Star Zero
If you're looking for a handheld Phantasy Star Online or loot-collecting action RPG, then look no further. While there are some setbacks, like the lack of certain shortcuts or an analog control stick, PSZ is still a great game. Even if you can't or won't play with other people over Wi-Fi or local wireless, the single-player mode is surprisingly engaging, with a slightly different take on the story depending on the race of your character. Phantasy Star Online fans may even find some interesting story tidbits in relation to those games.
#5 · Luminous Arc 2
There are better strategy RPGs on the DS, and certain aspects of the story may frustrate some people, but this game is quite enjoyable. The battle system is a big step up from the original game in terms of mechanics and difficulty. While the story starts to take itself more seriously earlier on than the first game, there are still quite a few chuckles to be had. Atlus's top-notch localization especially brings this out. Most of the characters are quite likable and memorable. The music is also very good, with Yoko Shimomura's contributions arguably being the best on the soundtrack. Imageepoch may not be a well-known developer yet, but its games tend to be very charming and endearing, and Luminous Arc 2 is no exception.