The cheese added a ton of flavor, especially the smoked Gruyere, while the onions made the dish even more delicious. This was by far the most flavorful macaroni and cheese I've ever had, and I thought it was very easy to make.
My only complaint was that the bottom layer of macaroni and cheese could have been a tad creamier — it was a little watery compared to the top layers. However, it probably would have cooked through more evenly with a little longer in the slow cooker.
In fact, after leaving it on the warm setting for another hour or so while I ate, it got even better. This would be a great macaroni and cheese for a party since you can serve it and keep it warm throughout the day.