Infinite Space is hands down the single best RPG adventure on the Nintendo DS. It's possibly the best game to arrive on Nintendo's dual screened moneymaker.
It's got almost everything you could want in such a game. An epic, galaxy spanning plot. A huge cast of memorable characters that really grow on you as the game stretches onwards. An amazingly huge world that will have you exploring for hours on end! And the game itself is incredibly long! Expect to spend over 60 hours on the game unless you're skipping everything to race for the end.
What the game doesn't have is a decent in-game tutorial, and it shows in a lot of the reviews you read here, and even in the professional gaming media.
Lots of frustrated gamers and reviewers complaining about the game's steep difficulty, how even the random encounters on the way between planets wind up being grueling. People claiming that battles rely too much on luck, with most of their shots missing entirely. Many people don't know about the fatigue bar, individual weapon ranges, character skills, fleet formations, and everything else that the battle system is built on. Crucial information if you want to get very far in the game.
To be fair, all that information is in the instruction manual, and in tutorial trailers released by Sega prior to the game's release, but let's be honest. Most people don't read the manual, and most people who get frustrated aren't going to go looking for a YouTube tutorial video. They're just going to assume that the game is insanely difficult. The game would be receiving much higher review scores if it had a proper in-game tutorial to explain everything you need to know.
The reality is that the game actually isn't that difficult at all, once you understand the basic gameplay mechanics. If you own the game, and gave up in frustration I'd recommend searching YouTube for those tutorial trailers. If you don't own the game, and epic space adventure sounds right up your alley, then I'd highly recommend Infinite Space. Aside from the lack of a tutorial, it's the best game to land on the DS in years.