Disclaimer: I have not been to the Loaf this season even once, so I don't have a first-hand handle on current conditions except by inference from the situation at nearby Saddleback. Also not a Sugarloaf "regular"; I generally ski there 2 or 3 times a year.
The Timberline lift buys you a few (two or three?) hundred feet of vertical vs. the top of the Skyline (formerly Spillway) lift. Timberline is a slow lift with a very flat pitch. The terrain underneath the lift is forgettable. True, it is the only lift-serviced way to the "top" (not really quite the summit) and to the front face above the Spillway Crosscut catwalk. These steeps (e.g., White Nitro Extension) can be fun. The snowfields can also be fun when conditions are just right, which they are very rarely in my experience. The reality generally does not match the hype, IMHO. The extra time you spend getting to the Timberline lift and then riding it is not worth the limited skiing you get out of it except once or twice in a day just for the experience of being way up at the tippy top. It is especially nice on a sunny April day when you can stand around long enough really to appreciate the view before getting frostbite. It is possible to hike up there from the top of Skyline if the lift is not running; I've done it. Not too bad.
The meat of the advanced cut-run skiing at the Loaf is served by the Superquad, King Pine (RIP) and (especially) the Skyline lifts. Generally on an ideal spring day you pretty much spend your time lapping King Pine and Skyline. (The run-out to the base of the Superquad can get slow on a warm day.) In really good late-season conditions (corned-up bumps) it's pretty heavenly to just ski Winter's Way (my favorite) and the six or eight other trails easily accessible from Skyline over and over. There is more skiing there than the trail map suggests.
As for comparisons to the northern Vermont areas you mention, I'd say it's comparable in size and challenge. Different in character from Smuggs and (especially) MRG, in that Sugarloaf is more open, with more groomers and fewer really narrow winding runs. Sugarloaf is more of a straight-up cone than Jay, with almost all the runs following a consistent fall-line. It's more like Stowe than any of the areas you mention. If you want a Mad River-like experience, Saddleback is a better choice than the Loaf.
All that said, the mountain will be running with only two of its four lifts serving significant terrain operating. So I would tend to stay away except on weekdays, notably during Reggae Fest next weekend. On Monday / Tuesday you should be fine, given a favorable weather forecast. (I haven't checked.)