Although I will be echoing some opinions here, hopefully this helps:
Mario and Luigi: Highly recommended. A must play if you enjoyed Paper Mario, Nintendo has done an awesome job of fusing platform like play mechanics with a fun and involving RPG...but the best part as someone else has said, the Mario world is brilliantly and hilariously realized.
Fire Emblem: I do beleive this series started tactical RPGs....but regardless it hasnt fallen behind the current boom in Strat/RPGs. Fire Emblem (this one anyway) can be considered a very involving tactical game with an excellent story and characters to warm up the package. RPGs are partially for story right? Dont overlook Fire Emblem....for the record I would percive this as having more "replay" value than the upcoming Shining Force: Resurrection fo the Dark Dragon. Dark Dragon has added some new characters, side quests, plot points and dialog....but these extend the original gameplay not call for replay. My roommate has played Fire Emblem at least twice without getting sick of it...
Shining Force: Here you really have to elaborate. Cuz, there are currently two Shining Force games on the GBA and soon there will be three. The first two are "action-rpgs" with multiplayer support and the upcoming game is a remake of the original Strategy RPG that kicked off the series. I dont know how the Action RPGs are, but you can read Planetgamecube or IGN for that. I beleive they were considered decent, but prolly not better than Secret of Mana: really not sure on this.
I CAN comment on Shining Force strategy RPGs....the upcoming game is Shining Force: Resurrection of the Dark Dragon and in a nutshell the gameplay is heavily inspired by Fire Emblem itself, as someone has pointed out already. You cannot expect the bulk of gameplay to be too different although for the record Fire Emblem is likely the more complex of the two as Dark Dragon, in terms of strategy RPGs, is significantly older. If what you really crave is walking around towns then yeah, Shining Force has that. Both FE and SF have inventories and special weapons to manage, so getting cool powerful weapons is present in both. In terms of plotline and character development, well I have not played this specific Shining Force so I cant comment directly. Indirectly however, Shining Force games are of the same standard "save the world from evil" fare, but I am confident this will be pulled off in an enjoyable fashion. In fact, I believe the dialog was rewritten. This remake sports upgraded graphics and a branched out storyline with more side quests and characters.
To sum up FE vs. SF, I would bet on FE as the overall better game, but I have fondness for SF as well and I beleive you cant go wrong with that either, especially if walking around the overworld and towns is an important aspect for you. But understand, the bulk of gameplay is tactical for both.
If indeed what you want is a traditional RPG and you dont have the patience for strat/RPGs, well you'll have Final Fantasy 1+2 upcoming which has been greatly enhanced, Lunar (which has been somewhat dumbed down from its original incarnation but is still a worthy RPG with a great story) and the Breath of Fire ports. You can also track down a copy of Lufia:Ruins Chasers (?), the GBC game. Now THAT is a long and involving traditional style RPG...but good luck finding it.
Umm...what else can i say....you should give those strat/RPGs a go however, the difference due to characters and storyline are significant when compared with FF:Tactics. Tactics Ogre also is an awesome strat/RPG with probaly the most developed plot and story of all.
hope you find some handheld happiness bro,
-Blackknight131