My son was pretty excited when he got his Dragonborn Totem Barbarian to 15th level, grew a pair of wings and gained the (modified Eagle totem) ability to Fly!
If anything I am struck by how many new awesome powers Barbarians get as they level up, much better than eg Champion Fighters.
That's a good point about the Champion, but I feel it's simplicity is one of it's strengths. I have players that don't want to play anything more complicated. The 14 level Eagle totem ability is great, but it's more like a super jump than flight since you'll fall if you end your turn in the air. Still it's my favorite of the level 14 Barbarian options.
Wolf gets a knockdown, but I could always shove someone down since level one. being able to use it as a bonus action and with out a save is what I would consider getting better at something I could already do.
Bear gets to give incentive to enemies to attack themselves rather than their immediate allies, but Reckless Attack already gives incentive to all enemies to attack the barbarian regardless of whether their allies are next to term or not. It's still a good thing, but I don't consider it a new thing.
Elk totem lets the barb knock down, do damage to a target, and move, all of which it could do before, but now it can do them at the same time.
Tiger can likewise move and attack and attack, things it could do before.
Battlerager gets something new, but non-scaling 3 damage to enemies that hit it while raging doesn't excite me much.
Berserker gets to attack on a reaction when hit. Mechanically great, but it's kind of just another attack.
By contrast the UA Barbarians got Damaging Auras, the ability to change the terrain around them, a howling battle cry, the ability to Rage without dying... things I thought were new and more interesting. Maybe this just comes down to personal tastes.
It's still a great class, my favorite in fact. It has one of the best if not the best capstones, it's primary abilities of Rage and Reckless Attack work so well together it's a beautiful thing.