I was on it for a few months. Atkins, to be precise, since there are a number of keto diets. Atkins limits not only the number of grams of carbs in the various phases, it also lists which carbs you can eat.
As for experiences, the only tough part was induction, i.e. entering ketosis. After two days, my glycogen was used up, and that's when the notorious "keto flu" hit me. It didn't last long for me, only a couple of days, but I know one guy who had it for four weeks. Once that was done, and I was in ketosis, it was smooth sailing for the most part. Carb cravings did occur, but I learnt soon that they pass as quickly as they come. Weight loss was rapid in the beginning, as expected, because the glycogen was used up so quickly (along with the water that is stored with the glycogen). The weight loss stabilized, again, as expected, and I could really tell it was entirely fat, because there were significant changes in the way my body looked.
I didn't consciously come off it, it just happened. One day of not having low-carb meals available turned to two, and so on. I did not regain all that weight. After regaining a few pounds of glycogen and water, weight loss resumed, since I was still eating healthy, counting calories, and on the Intermittent Fasting regimen.
There were two other people I know who were already on the diet, and they told me to drink a lot of water, or you risk kidney damage. I worked my way up to a gallon of water a day before I attempted keto.
If you're willing to stick with it, it can be a great way to ease off the unhealthy carbs. Atkins does introduce healthy carbs in phases so that you're able to find your personal sweet spot, pun intended, where you're losing at the rate you want or maintaining. I'm off keto, but I still diligently avoid unhealthy carbs. Another thing it did was remove my fear of eating fat. It really isn't the enemy, junk carbs are.
One drawback initially was having no glycogen to lift weights. However, if you stick with it, you'll eventually be "keto-adapted," which is different from simply being in ketosis. There are many athletes who are keto-adapted and have no problems with strenuous exercise, because they're at a stage where their bodies burn fat, not ketones (which are a byproduct of fat usage), during exercise.