The section I've ridden quite a bit is the 7 or 8 miles from the parking area in Farmington, CT up to Collinsville, CT. The latter part of that section is quite pretty as it goes along the Farmington River. On the weekend, it can get busy with cyclists and walkers. Collinsville has a nice, quaint Main Street with a deli/coffee shop that is a popular stopping place for cyclists. While I've ridden the bike path a few miles north of Collinsville, I generally use that 7-8 miles as a warm-up, then go off on the back roads of New Hartford, Barkhamsted, Riverton, etc. I did meet riders who were putting together their own century ride by going up to Northampton, MA. It's definitely possible although I don't think the bike path is completed all the way through. I think you'll have to get off-path for sections. I've not ridden the trail below Farmington (i.e. New Haven up to Farmington).