I only played a little of DC and DC2, but from what I played, Level 5 learned a lot of lessons between the productions of the two. DC2 was definitely a lot better than the first one. That's my personal opinion though. It's probably because of the expanded options and all of that stuff. That, or I'm just a whore for graphics. Or something.
As far as Rogue Galaxy goes, it's probably the only Level 5 game I've played through completely. It was, at the least, a really great game. Tons of options, and tons of content. The characters, especially the protagonist, were probably the best I've seen in ages. All that being said, the story went fucking south fast, which was a major turnoff. If they hadn't screwed it over so vastly, it probably would be one of my most favorite RPGs ever. But uh, when Desert Claw revealed who he was to Jaster, I literally could not play that game for a month. And no, that is not the only instance where I was utterly repulsed from that game. I guess my main gripe with the game is that it felt like the entire second half of the game was rushed.
Of course the game's saving grace, once again, lies in the gameplay(which is... really odd for an RPG?). So much so, that I was thinking about playing it again. I'd probably play it up until the second fight with Seed(GRAWGRAHGRAWHR ANCIENT SUPERPOWERZ PULLED OUT OF MY ASS GO!), and then never touch it again.