Is Niseko too crowded to be worth visiting?

Busy, yes. Not worth it, no. It's the resort most first-timers end up at for good reason, and the reputation for crowds is earned but overstated by people comparing it to Japan rather than to the rest of the world.

Niseko genuinely is the busiest resort in the country: the roads clog in peak season, first-lift gondola queues can run 45 minutes, and a powder morning is tracked out by 11am. Set against a big US or European resort, though, it's mild. The crowd also thins out fast once the first rush is over; you're rarely properly stuck for long, just competing for the best snow early.

What you're paying for with that crowding is the thing most alternatives can't match: near-universal English, four linked areas on one pass, and lodging and lessons that don't need a translation app. If none of that matters to you and you'd rather trade some polish for space, Rusutsu is 40 minutes away and handles a busy week noticeably better than Niseko, since its layout spreads skiers out rather than funnelling them onto the same runs. Kiroro is quieter again, with next to no queuing outside a short gondola wait after lunch, though the trees are more tightly controlled.

The honest split: go to Niseko for your first Japan trip, or if ease matters more than solitude to you generally. Use it as a base and day-trip to Rusutsu or Kiroro if you want a taste of both without giving up the convenience of staying somewhere with everything sorted.