Whether you pick up Sega CD Lunar: Silver Star, or PS1 Lunar: Silver Star, you're getting a real RPG. The PS1 version cuts a lot of the fat, but it also weakens several key scenes (and Ghaleon isn't nearly as cool in the remake). I prefer the original, but both are respectable.
Lunar 2: Eternal Blue is a different story. The PS1 version is barely a real RPG, mostly because the dungeons are so linear... not just by comparison to the original version (which had some of the most amazingly complex dungeons in any JRPG) but by comparison to the first PS1 game. Also, the cinema scenes are better on Sega CD. They're essentially the same from a design standpoint, but the colors are brighter on Sega CD than on PS1, and the original lacks the remake's heavy artifacting.
Finally, the difficulty was screwed up. In the original, each character's "terror from the past" boss was insanely hard. In the remake, those guys are super-easy and the hardest bosses are a bunch of random dragons. Boo! Hard bosses should be meaningful characters. The Eternal Blue remake is an example of how to take one of the greatest RPGs and make it one of the lamest -- the story survived, but the game used to be so much more than a vehicle to tell a tale.