I skipped the Big E for several years during the late 80s, early 90s, because it always seemed like more of a marketplace than a fair. Once I started going back, I haven't missed one in several years and I can't wait for next year.
The entertainment choices have stepped up. Up and coming and chart-topper acts are the norm, more often in country/western pop it seems, but that's ok.
The merchandise exhibitors are many and varied, so chances are you will find something you want to buy.
The food choices are through the roof and there's a great selection of beers.
The state houses (one building dedicated to each New England state) are loaded with the specialties of each, including food and apparel. And some of that food is fantastic (think Maine lobster roll). Prices are reasonable to slightly high, but that's to be expected.
The parades are great, including a Mardi Gras style with beads and candy thrown to all who stand on the sidelines.
There are farm exhibits (animals and vegetables), horse competitions, etc etc. The Clydesdale horses are amazing. You can even visit the stables and get up close.
I could go on and on, but you get the picture. I usually park far enough away to pay $5 or less to park, and yet close enough to walk. Plenty of the neighbors will park you on their lawns or business lots.
It's worth the trip. Be sure to wear comfortable shoes as you'll be doing a lot of walking.