I like Sam Adams in general, especially Latitude 48, but their Oktoberfest seemed a bit disappointing for me...not sure what it is exactly.
Lat 48 is really good. Sam Adams is my "go-to" beer, i.e. something I buy and drink on a regular basis as a day-to-day beer.
Some things you might think of regarding oktoberfest. Not every brew is the same. Yeast, heat, hops, grains, etc can all vary a bit. Sam A is pretty consistent, so it might not be that in this case. It's more common in microbrew. Another thing I learned over the years is that I change my taste over time. Something I like today, I might not like as much next year. Also, depending on mood, weather, time of year, stress, and what I had for dinner, the enjoyment of a beer changes. Perhaps you just haven't figured out what food works with the Oktoberfest.
Oh, and I forgot, the age of the bottle too and if it's been in heat or kept cold in transport.