I've only been playing 5e for a little over a year.
I think that the rules are quite simple. The only thing which is somewhat complicated is to determine what feats, class feats, archetypes, possibly multiclassing to combine at which point of time and in which order to meet certain objective. As such, the net seems to be full of stuff on how to do just that to become a "demigod" at level 20.
However, I believe that the most important levels one should care for are Tier 2, i.e. Level 4 to 8. In Tier 1, the system can make character's lives dangerous and short. Some campaign never reach Tier 4, so why should I primarily bother what my character will be finally able to do if everything is almost over?
Besides that, I find D&D and 5e overpowered. It is a high fantasy, high magic environment, where the characters are pulled into situations time and again to "save the world" or at least "save the kingdom". Too much bling-bling, less would be more.
Yet, much depends - needless to say - on the DM. Even with 5e you can play a campaign which is remotely down to earth. But it is much more difficult in this system and its background, than in others.
As for D&D 5.5 or "One D&D", I remain reserved. New rules versions of D&D have mostly not been modulations and modifications of the given system but rather rules rewrites. 5.5 claims to be compatible with 5e, but if this will really be the case remains to be seen. In general, I do not like to have to (re-)learn a roleplaying system every 10 years ago for a favored gaming world. On top of that, this leads to many stuff one has procured becoming obsolete or only usable with tiresome adaptations. Opposed to that, ASL (the tactical wargame, not a RPG) is a fine example how a game with extremely complicated and diligently crafted rules can persist for decades with only minor changes.
As such, I will probably get the new 5.5 PHB just to get a feel for it but beside that stick to 5e (and the 25 printed publications which I have for it).
As a background:
I have played roleplaying games for close to 35 years and mastered several campaigns that ran for maybe 10 years. Mostly Rolemaster on Middle Earth and Midgard (a German system), then some Call of Cthulu. I think very highly of Harnmaster and Harnworld - D&D is definitively not even near of a match. Alas, I had no opportunity to play Harnmaster despite having around three feet of shelf room of it. With life running its course, it has not been possible to maintain the old campaigns alas. When I was asked to join a 5e campaign which is run via Foundry & Discord and nothing else currently running, I took the chance. Foundry, Roll20 and the like are amazing tools that I was curious about. Yet, I believe that the good ol' pen&paper at the table is superior: In the classic playstyle, there is much more theater of mind. It creates my own pictures of things in my head rather than presenting me computergame like graphics out of the box.
von Marwitz