Okay, I gave this another try based on Devin's comments about what might've gone wrong the first time with the stringy cheese and the bland flavor. I followed the recipe to the letter except 1) I only did a scant cup of elbow macaroni, in case I had too much pasta last time and there wasn't enough sauce for the dish which could've led to the blandness problem and 2) I was super careful not to overheat/overcook the cheese sauce. When I heated the milk/flour mixture and the cheese, I had the burner on low and was stirring the sauce as the cheese melted. At first everything looked okay but then the liquid started to separate from the cheese. In baking (with butter), that's usually a sign that the mixture is getting too hot. The cheese wasn't completely melted yet and I'd been whisking all along so I didn't think it was too hot. Just in case, I took the pot off the heat and whisked until the cheese had completely melted in the residual heat. The sauce looked good and was creamy. It definitely wasn't as stringy as before. I added the elbow macaroni and kielbasa and stirred it all up. It certainly looked better/more "saucy" than my previous attempt a couple of days ago. I could taste more of the salt so it wasn't as bland.
But I'll be honest - it still wasn't as creamy as I had hoped. I'm going to blame the low-fat Cabot light cheddar cheese. While attempt #2 wasn't as stringy, the pasta with cheese sauce did clump a little once it was cool and this time, there was a little bit of liquid separating from the cheese again. That didn't happen with the first batch so not sure what's up with that. In general, this recipe was okay and I certainly don't mind having it for lunches next week when I go back to work. Not sure I would make it as a "company" dinner though. On the plus side, I really appreciated how easy this was to make. This is easily something I could throw together after work instead of just microwaving the nearest frozen dinner. I'm even glad I "failed" the first time and thank you, Devin, for your comment and tips on how to make it properly. I learn more from my failures than I do with successes. Biggest takeaway for me with this recipe and with using the Cabot light cheddar cheese was not to overheat it because it will get stringy.