I have an Opinel no.8, and it was the knife that truly changed my understanding on knives. Looking back, I only believed I liked thick blades on folders due to hype. During the little time that I have been into knives, the thin blade of the Opinel is perfectly tailored for the very tasks that I need a knife for. Noticed some comments on flexibility, mine does not seem to flex really though. I mean, I can get it to move a bit if I hold the tip and yank on it, but those types of forces are not experienced in any of my chores, so it stays completely straight. Only bad thing about them in my opinion is that when you wash them, it is too easy to get water on the handle. One drop and opening and closing the blade gets quite laborious, relatively speaking. It would be nice if they offered some nice synthetics that still retained the look and feel, but without the whole issue of swelling.
I did notice that you mentioned in the post that you use oil on your handle. I need to start doing that.
Back to what is great about them, I like how every centimeter of the blade is sharpened, no need for a choil. The fact that the wood adds a decent amount of friction when opening means that the locking ring does not even need to be used for me most of the time, which is nice. The ergonomics for the 8 are almost perfect for me, and few other folders in my experience have a full three dimensionally shaped handle.