A lot of students are unprepared for the step up in intensity & seriousness of 2nd year. The marks count! This can be scary. And academics' expectations that they start to really take on the independent learning we require.
But students need to remember that learning is cumulative and it's a process. And learning is difficult, if you're really pushing yourself. So sometimes students project fear or unhappiness with their achievements onto other things: the course, their tutors, and so on ...
I found my 2nd year the toughest year BUT it was toughness I wanted -- that was why I was at university. I have never been under the illusion that learning complex stuff isn't difficult. Really, what's it worth if it's too easy? The struggle is the learning.
but he's frustrated that he has so much to do that he's not enjoying the subject as much as he was
Personally, I don't get this? What does he mean by "so much to do"? I know I sound like an old fogey, but students don't read enough nowadays. In my first degrees (I did two overlapping) we read at least one substantial text each week, plus other stuff -- usually a big novel, and a philosophical text or work of history, or the equivalent. So I really don't buy the "too much to read." That's generally what students are at university to do.
As for feedback: I think it's important to work out what any student means by feedback. Do they mean the grade? That's actually not feedback -- that's simply the number.
Feedback comes in many forms: narrative written feedback with returned assessed work, but also feedback in terms of seminar discussions & debates. Often students don't think this way, and they miss out on opportunities for reflexive learning. For example, if you participate actively in a stimulating discussion in a seminar, and come away with your brain bubbling with ideas, then that's feedback -- it suggests you're firing on all cylinders and learning actively and your ideas are productive and others engage with them.
And yes, OP, your son can book a personal tutorial any time, or see a tutor in their office hours. This is also feedback.
Also, you use the word "disappointed." What else does he do? Is he pursuing the wonderful opportunities for extra-curricular engagement? I think that extra-curricular excellence is a really significant thing in a "good" university. Or is he able to do some volunteering, an internship, or a work placement?
I guess my advice is that your son think about why exactly he's disappointed -- is it just that his essays haven't been returned? There could be admin reasons for this, so how could he get the feedback in another way? First stop would be the tutors teaching him for the modules concerned.