Meh, I still don't like Lagaan. I wince every time he says "Neptune's beard!" That's a really stupid curse.
I dunno-- is it any sillier than "Great Krypton!" or "Great Caesar's Ghost!"? Actually most curses are silly once you deconstruct them.
Now, the constant aquatic substitutions for standard expressions (especially ones that didn't make sense)-- that got old. "It'll be a piece of crab cake!"
Still, I guess he grew on me because between his goofy puffer-fish ability, his unimposing code name (what kind of name is "Lagoon Boy"??!!?) and his general attitude, I didn't expect much out of the character. I expected him to be the team joke, the lame-o who barely pulls his weight -- and it turned out he was pretty darn effective. Even if he's still a jerk.