I'll preface this review with 2 caveats: 1) I've only been to one other resort in the northeast, so my perception is relative to the smaller mid-Atlantic resorts and the I-70 Colorado resorts where I've done most of my riding and 2) they hadn't gotten any snow in a week, so conditions were less than stellar, but I'll try not to hold that against them.
Overall, Sugarloaf has a really unique feel. It is very decidedly a local's mountain; everyone seems to know each other. There's not an outsiders-aren't-welcome vibe, but the other skiers aren't going out of their way to be friendly on the lifts or anything either. The bulk of people are middle-aged, advanced skiers. There are very few snowboarders, not a lot of young poeple, and hardly any novices. I'm not saying any of these things are good or bad; they just give the mountain a different feel than anyplace I've ever been before.
The mountain itself offers a great variety of terrain. The groomers span from shallow to seriously steep. There's a great variety of mogul runs, running from shallow and small to steep and big. Even with no fresh snow, there were still a few runs with nice soft bumps (Ripsaw was my favorite). The glades definitely leave something to be desired though. The trail map marks tree-runs all over the place, but most of them are relatively inaccessible, either with a single entry point or very steep/tight. There's hardly any open glades; it's pretty much experts only. The expansion should change that, but for now, getting back to the lifts from Brackett Basin can be tricky, and you're looking at a long commute back if you miss it. The Snowfields should probably be called the Icefields right now, but I'm sure they're sick with some fresh powder. All in all, you really have to be advanced/expert to appreciate what Sugarloaf has to offer. I docked a star for the glades, but otherwise the terrain is great.
One thing I found upsetting is that they leave terrain open that's severely lacking in coverage. That's fine, but there needs to be some kind of warning, especially on a groomed run. I got some serious gouges on my board on Binder when the snow suddenly gave way to a gravel pit.
The lifts are so-so. The Super Quad is nice, but lines got pretty long on Saturday. The Double Runner and Spillway lifts are SLOW, and Spillway East is closed for the foreseeable future (possibly for good). The setup makes it pretty much impossible to do laps on the Snowfields; you have to take two lifts to get back to the top. There's a lot of cross-cuts to get to different parts of the mountain. They work well, but there's definitely a learning curve involved. Once you figure them out and where you need to keep up speed, they're fairly easy to use, even for snowboarders.
My wife and I both took lessons and they were great. Her group had 4 skiers, and mine was just me (chalk that up as an advantage of being a snowboarder on a mountain of mostly skiers!). My instructor was friendly and did a good job of explaining what I could do to improve my technique.
As far as the rest of the resort, it's a pretty chill place. The staff was all very friendly. We stayed at the Inn. It was cheap, so you get what you pay for, but it got the job done. Other reviews have mentioned it, but I'll re-emphasize, there is NO nightlifte at Sugarloaf. The bars are empty by 8pm or so, except the Shipyard, which is and older, local crowd. If you're looking to meet people and party, this is not the place to be. Sugarloaf is for skiing, not apres-ski.
Oh, and try the Bag Burger... it lives up to the hype.