The JMT is a mosquito-ridden dust-slog up incredibly steep slopes covered with little ball bearings disguised as pebbles. If you do survive to reach the pass, all you can see is more rock. Savage bears, sneaky marmots, and silent rattlesnakes lurk nearby, just waiting for your first, inevitable stupid move. The abundant deer (see "hunters" below) and grouse are their scouts, sent to locate potential prey.
Most water crossings are readily and preferably swimmable; packrafts are optional.
Escape routes are almost as bad and take at least 2 days, being their own mini-versions of the JMT tread. Did I mention the rampant hunters that stalk the woods, desperately seeking something at which to fire their new rifles?
Resupply options are almost non-existent since the outrageously overpriced horsepacking outfits have bought up and closed most local roads - of which there are pitifully few - and towns, which they use to shelter the stuff they rake out of their horse barns.
Yosemite Valley? It's a tourista trap - lots of loud kids and rude parents in shorts and Hawaiian shirts packing 20 pounds of camera gear they have no idea how to use. Concessionaire price shock is the #2 cause of sudden death in the Valley, second only to being run over by shuttle buses driven by under-paid, legally blind, former NASCAR drivers.
Mt Whitney? Yes, it is the highest point in the lower 48 states - that part is true. What they don't tell you is that Sir Edmund Hillary decided Everest was an easier and safer climb. The only rangers that go there are the ones being punished by their superiors for morality reasons. Forget the ice axe and crampons; bring oxygen tanks - lots of them.....and be sure your life insurance premiums are paid in full.
Decades ago, the western states decided that it's cheaper to just drop their convicted psychopaths and serial killers in the middle of the wilderness and let nature take its course. If they're innocent, they will survive, if not............ Unfortunately, a few have proven stronger than the local wildlife and even the Grizzlies and rattlesnakes turn and run.
Be smart - stay away. Better yet, stay east of the Rocky Mountains. This is the REAL wilderness out here.
The rest of you posters, STOP pontificating; let's keep our secret to ourselves. We don't need no stinking east-coast hikers.
I'm told the Long Trail is nice ... and it's local. Hike on!