Gandalf (or Mithrandir, or Olórin, though I most definitely prefer Gandalf) is an Istari, one of the Wizards from over the sea sent to Middle Earth to hinder Sauron.
Gandalf is an immensely powerful Maiar, who, although required by both the Valar and narrative need to keep his true might cloaked, can still kick Balrog butt if so needed.
Gandalf, after being returned to life as Gandalf the White following his fatal battle with said Balrog, is the one to break the staff of the great wizard Saruman, and is also a pivotal player in the defense of Gondor, in the days leading up to the destruction of the One Ring.
Gandalf is all of these things... but we do not love him for them.
We love Gandalf because he is a friend of the Hobbits, because he likes to lounge about on hillsides smoking the finest weed in the Shire, because he is a lover of fireworks, because in addition to his understanding of wizardry writing he seems to have picked up somewhere the door rune for "burglar," because he'll drag Bilbo, on pure whim, with him and twelve dwarves on a quest against a dragon (and Tolkien's dragons were not to be taken lightly), because while others can blow smoke rings he can blow smoke ships that sail through smoke rings, and because even as Gandalf the White he still had that twinkle in his eye at just the right moment.
Tolkien went on and on and on and on about the beauty and wonder of the elves. Screw the elves. Legolas was the most interesting of the lot, and I'd say primarily because of his friendship with Gimli. Now matter how many la-la-la-lallys they spout on the borders of Rivendell, elves are dull, and that's when they're not being insufferably snooty, full of themselves, and even a bit racist in that special way only a thousand-year-living elder race can achieve. Of all Tolkien's creations, Hobbits, Dwarves, Ents, Tom Bombadils, even Orcs are more interesting than those point-ear jerks. But my favorite among all his varied characters is Gandalf, who despite all that talk about secret flames and names seems to me to be basically a somewhat wise, rather mischievous old fart who's no good at guessing passwords. Don't ask him to crack a server, but you couldn't ask for anyone better to send off a 111-year old Old Friend in fine style. Argue if you want that all that stuff was a sham, I respond that the falsest lie contains some truth, and that you cannot convincingly pretend to be anyone except, in some deep corner of your soul, who you are.