Volibear does much more damage to squishy targets and is far tankier than Udyr. You pick him over Udyr for his teamfighting, and you pick him over Olaf for his CC. Problem is that most people build him like any other tank: Cinderhulk/Sunfire > Visage > Deadmans > ect.
Stick a Titanic or Righteous Glory into his build and he's like a completely different champion. Glory lets you abuse your lead and dominate the midgame, whereas Titanic is safer and scales well late. It synergizes perfectly with Voli's kit and allows him to easily 100-0 a squishy target at just 2+ items.
Tiamat and Cinder together also help out a ton with his slow clears.
Volibear top takes some getting used to, he has a few rough matchups. Mainly Kennen, and Teemos that don't randomly poke with Q. Rumble and Kled are fine. Against rumble simply play safe until you get your mr/health items. Against kled it's pretty easy to all-in him at 6. Use ult to dismount him, then chomp him as he attempts to get skarl back. Kled ult just doesn't give the same dueling power as voli's.
He is my champion when i absolutely want to win. I have all the tools I need to gank or turret dive, there's little pressure on me to end the game early. Voli (with the titanic build) scales very well into lategame. My only complaint is how "slow" his earlygame feels. He clears healthy but it takes so long to kill camps until you get your cinder. This gives faster junglers like Graves/Rengar/Kha/Ivern a head start over you.
tl;dr He's middle of the pack as far as junglers go. He's nowhere near as bad as Udyr, Kindred, or shudders Rek'sai, but he isnt top tier either. Other champs need attention more than he does.