Rather than a grind, I'd call it a "loop." I wouldn't call it a grind since there are always like several alternate paths to explore and make meaningful progress while you become stronger and stronger. And it's not just becoming stronger, but expanding your options, I.E. collecting rupees and materials to craft new badges or new potions that can allow for fresh strategies on a mission that was giving you trouble.
I totally agree about continually discovering new favorites. Last night, I discovered the joys of Twili Midna's fully charged twilight meter (not to mention conjuring up huge laser cannons, flinging bridges out of wormholes, riding atop a shadow-wolf, shedding a single tear that shatters space-time, etc). The night before that, I was really into Ruto, from her running animation (swimming through the air!) to her various acrobatic maneuvers and AOE attacks. Prior to that, I was really into Fi with her graceful pirouettes, and prior to that it was all about juggling fools with repeat hammer strikes from Darunia.
Through it all, I consistently enjoy Impa with her naginata (probably my favorite, and the fact I love both her skins is a plus), and Ganondorf, who just exudes raw power and ruthless rage with his hard-hitting attacks. Those same qualities endear me to Volga -- the attack where he turns into a dragon and dive-bombs the battlefield hits like a nuke -- and I've also taken a liking to Cia and her scepter-whip and summons. Speaking of summons, how about the hilarity of conjuring up boss monsters with Lana's summoning gate, or the ever-reliable cube-rolling with her spell-book? She's downright charming, too, in her Skull Kid outfit and her Guardian of Time attire.
And there I go again. So many great characters in this game. All of them look and sound wonderful, and are a blast to play. The only one that hasn't "clicked" with me yet is Agitha, and even then, I adore the fact such an unorthodox fighter is in this game.