Mario and Luigi 2 was a piece of shit. The game was extremely boring, extremely repetitive, and made artificially long by having enemies with huge HP. Not that battles were a challenge: once you mastered the piss easy timing defense scheme, it would almost be shameful to lose any HP in a regular battle.
M&L3 has an interesting premise but it doesn't sound like anything changed, battle or gameplay wise. Better luck next time, Alphadream.