Personally, I liked Superstar Saga better than Partners in Time. To me, PiT seemed like they did too little with the present day, and too much to make the past aspect a reliable storyline.
Not to mention they removed the most amazing aspect of battle, Bros. Moves (for those of you who do not know, special attacks that incorporated Mario and Luigi tag-teaming an enemy in a fantastic display of cooperative attack techniques and splendid sprite-age) and replaced them with Bros. Items, which did not have the same pizazz as the Bros. Moves, and the older bros. could not use hammers like in the previous game...which made it seem empty.
Mario and Luigi 3: Bowser's inside story looks good, but I'm worried about the fact that Mario and Luigi will not be incorporated as much as the previous titles, having their game-play mostly inside of Bowser and mostly 2-D (I love platformers, but the 2-D kind of takes out of Mario and Luigi RPGs.) makes it seem less....Mario and Luigi to me.