The reason it didn't turn out too well, in my opinion, is because the sweetness of the filling clashed with the acidity of the tomato sauce. (It could also be that the textures didn't enjoy one another that much.)
Browned butter and sage is also my suggestion. The Parmesan on top is great, but if you are trying to keep your saturated fat intake down, it's not going to break the dish. I had the pleasure of eating that dish just a couple of weeks ago. This was the Saturday after Thanksgiving and I'd overeaten two days in a row prior to that. It didn't stop me from eating every bite. (Like the pizza cat, I regretted nothing.)
I generally don't go for sweeter entrees, but this was good. The Parm and sage added enough salt and savory that it worked. If you are the type to enjoy sweeter things, try a simple white sauce with some nutmeg and maybe a dash of onion, like you'd toss with creamed spinach.