I don't have a .35 Whelen yet, but I plan to someday. It falls kinda between the big bore lever gun cartridges (.375 Win, .444 Marlin, .45-70) and non magnums like the .30-06, .308, and .270.
With a 250 gr bullet at 2500 fps mv, it should work for any North American game animal out to about 150 or 200 yards, longer for deer-sized critters.
I think it would be perfect for someone who wants one rifle to "do-it-all" but doesn't want to put up with the recoil of a .338 or .375 magnum.
It's probably at its best for hand loaders, as factory loads aren't common or cheap.