Bluff and Haley are definitely worth the time. Bluff has some nice trails, and I do see guys and gals there with your style of bike (I'm assuming given your forum name). There's not a lot of steady downhill, but a good bit of rock and exposed ledge to play around on.
Haley is connected to Bluff. We usually use it for a warmup loop, not nearly as much technical there. It's worth going for the views though, it's on the edge of a cove, you will see shore birds and osprey, going through the meadow you occassionally will see red tail hawk.
Moving away from the immediate Mystic area, you have:
Oswagatchie Hills, new area, very well blazed trails, some very technical spots that I think could challenge anyone, though I am a bit of a newb and an old (47) careful cross country/trail rider. This spot is in Niantic and that's a seaside town worth a visit, less touristy than Mystic. Check out the Black Sheep for a nice beer and lunch.
Hartman Park in Lyme/Salem. Lots of rock, technical climbs and descents.
The various trail systems off of the Airline Trail, a rail-trail in central/eastern CT. These include Salmon River State Forest and Grayville Pond.
Moving east towards Rhode Island, you have Burlingame, Big River and Arcadia. Of these I would say the one most worth a visit is Big River. Not because the other two aren't fun, in fact overall Arcadia might be a little more fun. But rather because much of Big River lacks the typical New England glacier remnant topography. Not much in the way of rocks, more pine forest with sandy soil that berms up really nice. There are swoopy section there you can really fly though.
I know Bluff very well, the other places I tend to be following others. You really can't get lost at Bluff or Oswagatchie, so I would encourage you to go there if guideless. If you want a guide for Bluff drop me a line and I'll see what's up. I have family stuff going on part of this weekend, not so sure about next weekend. I live close so I'm always a possibility for a mid week ride as well.