My wife and I have identical rigs with only one difference. I few months after building them, I added an SSD to mine. With Windows 10, there is in fact a noticeable difference in boot times, though not near as severe. In games, it really depends on the game. Some games there is no difference at all and other games a very large and noticeable difference.
As for if it's worth it, that really comes down to a case by case basis. Some people make it sound like they are 100% completely mandatory in any build and if you don't have one you should get one immediately. Other people make it sound like they are absolutely unnecessary and not needed at all. The truth is somewhere in the middle. In most cases, yeah, getting one is really nice, if it fits in the budget. If you need more space than they offer because you store a lot of stuff, then you still need a standard HDD and if adding the cost of an SSD breaks your budget or causes you to have to sacrifice elsewhere in your build, it's not worth it. If you do your build and a few months later want to add an SSD, it's worth it.