I took two and a half years because I quit halfway through the third. My university had switched that year from quarters to semesters, which was bad news for Japanese classes because it meant we went from four days a week to three, and that's on top of at least four other classes and their collective homework (whereas on quarters you had longer/more frequent classes but the general minimum for full time credit was four). This was also the same year I had switched to an entirely new major in a different school within the university, and I found myself struggling to find time and motivation to focus on both Japanese and my major's classes.

I've since graduated from that major (Digital Media with a focus on video game development), and I regret it. I took a course in an underdeveloped major track with only one instructor, who was a cool enough guy but not great at teaching. If I could go back in time two years to when I was still taking Japanese, I'd have put the focus on that instead and either switched to a major in Japanese or focused more on animation and graphics.

However, not only have about two years passed since I stopped learning Japanese (and therefore keeping myself immersed in it), I feel that the classes and textbooks themselves caused me some trouble. At the time I thought it was all my fault for being lazy and not studying enough, but in my time researching self-study options and learning references, I've found out that maybe it wasn't all me. Basically my classes were guilty of all the traditional methods that rely more on how Japanese children would be taught, along with teaching from an English-speaking perspective (trying to fit everything neatly into a direct translation from an English equivalent, even if there technically is none).

Don't get me wrong, I did learn a lot in those classes, and years of watching subtitled anime did give me a slight boost in the beginning. But the textbooks we used were thick with grammar minutiae that made figuring out what was most important to focus on difficult, and the grammar itself was laid out in rigid fill-in-the-blank tables that in the long run made it hard to form complex sentences or actually understand why a you had to lay out a sentence a certain way (as it turns out, most of the time you kind of don't). And we only spent one or two weeks on each grammar point & sub grammar points (alongside a long list of new kanji and vocab), so a lot of it came down to cram memorization, take a quiz on it, then promptly forget it.