Some games benefit more from an SSD than others. Some might load two or three times as fast on an SSD, while others will be barely affected. A lot of it comes down to how the games load their data files, and how those files are compressed. You can find load time comparison benchmarks between hard drives and SSDs for many games, though keep in mind that they can vary based on the system's other hardware and graphics settings. If a game is unpacking compressed data, for example, it's load times could be more limited by a slow CPU than by the storage device. Also, the area near the start of a hard disk's platters will be faster than that near the end, so if a hard drive is mostly full and everything's in one partition, a game's files might get positioned near the end of the drive, slowing their performance.
https://www.youtube.com/watch?v=vCItBX8288Y
Here's one video showing some examples of load time differences between an SSD and hard drive in some relatively modern games on a system with somewhat lower-end specs. They provided links in the description to jump to each of the various games tested, in case you don't want to sit through the entirety of a video containing nearly 15 minutes of load screens.