1G was analog.
2G is networks originally designed primarily for calls: technologies include GSM (with GPRS+EDGE added for packet data), CDMA 1x or iDEN
3G is networks evolved for decent data speeds: technologies being UMTS (later upgraded with HSPA) or CDMA EV-DO
4G is embracing a data-only network: the technology being LTE (although some US carriers brand HSPA as "4G" to compete with WiMAX which was branding itself as 4G while having HSPA-like speeds)
5G is still kinda up in the air, but the focus (aside from faster speeds and lower latency) seems to be on more pervasive connections (better roaming between network types) or low power/IoT stuff
All these definitions are contentious. Some people say the initial LTE deployments weren't real 4G, but only LTE-Advanced is, etc.
5G NR is still OFDM based.
From a consumer perspective, upgrading the number means "the same, simply better and faster". (just like an iphone :)
The truth is probably more complex than that.
From my experience, 4G was much more reliable that 3G has ever been. May be the service providers have improved. But I have the feeling that 4G is a fundamentally different technology from 3G. In that case, is 5G fundamentally different from 4G?