A good rpg is one that has unique terrain. Most rpgs i've played are just one dimensional: you just simply walk along this one long long corridor and just kill whatever is in the way and when u heal, u need to walk all the way back to heal. This most resembles those Lotr RPGS i've played. Those rpgs i would say are big no nos to me. Dont just make dull paths with preplaced units; add flavor and spice it up. The terrain and preplaced units are what i think make the best rpgs. Give the rpg a tone, one that can easily get you into the game. Most that i've played really dont have a "mood" to it and gets me bored right away. And when you place the units on the map, dont just place all the bad guys there will be in the game, make surpise spawns, traps, huge mass attacks, etc. Make there be two opposing forces in the rpg - one being the bad guys and the other being like some sort of resistence or town. Interaction between opposing forces i think makes rpgs really fun.
music is kinda cool when ur battling boses and sometimes u can add ur voice for the evil guys with the text so player can see and hear whats going on... dont make it so everyone always starts with same hero and a hero selection.. cool spells are nice... an original storyline and maybe have a random ally get mission objective changes and they say something like once the final boss is done u auto unally and have to kill ur team to win.. they hve to kill u to win... have spawning locations but dont make units spawn like crazy cause then its easy for noobs to get lots of minerals and levels and stuff