I'm not exactly sure how to answer the original question. I feel as though a lot of factors go into my feelings toward a particular system or game, and I'm honestly not entirely sure that I completely understand my own mind when it comes to that.
D&D-wise, I started with 3rd Edition. I was happy to play that for quite a while, but I feel that it benefited from a combination of novelty value and my lack of familiarity with other game-mechanic styles. While I did, at some point, notice issues with how the game worked, I just kinda accepted them as part of how a tabletop game worked.
4th Edition was a mixed bag for me. It somehow managed to simultaneously fix the problems I had with 3rd Edition while also removing elements of 3rd edition which I highly enjoyed. I would say that I was content enough with 4th as a player to mostly enjoy it, but it was also the game which prompted me to look into how other systems did things. From the DM side of things, I liked the mentality behind encounter design and the plug-and-play aspect of how things were generally built, but I also struggled to find a happy medium between the stories I wanted to tell and the "physics engine" (for a lack of better words) underneath the 4E gameworld. At one point, I started fiddling with the numbers to try to make things work more how I wanted, but eventually it became easier to just run a different system. Oddly, I'm in the minority of people who liked a lot of the 4E cosmology changes.
I think I played 3rd and 4th for roughly the same amount of time, which was somewhere between 5-10 years for each. I would need to go back and think about dates and times for a more exact answer. Though, for whatever it's worth, I likely spent more on 3rd and bought more of the later books than I spent on 4th. I stopped buying new books fairly early in the life of 4E.
Pathfinder had a very enjoyable, but also very short-lived run among my usual group. It fixed just enough of 3rd to be enjoyable early on (and the boxed set with the goblin adventure was fun), but eventually some of the issues the group had with 3rd still popped up. I vaguely remember the group's last PF game going somewhat haywire due to issues with a Summoner PC being somewhat broken. I do still buy the occasional Pathfinder product (see below). Overall, I'd say PF lasted roughly a year.
I'm not exactly sure how to express where I'm at with 5th. I wouldn't exactly say I'm tired of it. I still generally enjoy playing, but I play less frequently, and -similar to 4E- it's been quite a while since I've bought a new book. I enjoy 5th, but I might categorize my relationship with 5th as being more casual and more shallow.
In contrast, I've been playing the same edition of a different system (and growing more fond of it) since shortly after D&D 4th came out, and I am not tired of it. If anything, my increased familiarity with it means I'm doing more with it now. It's a "modular" system (and I've gotten fairly proficient at building things with it), so I sometimes buy the occasional older D&D module or Pathfinder monster book or whatever so that I can convert an idea I like to the system. (note: I'm not specifically naming the system because I do not want to detail the thread by getting off the topic of D&D.)
