You can only play shyvana if your laners don't suck balls (if you have this assumption in solo queue, you are very brave). You can easily outfarm and outlevel your opponent to pressure dragons and buffs. Only real skill to playing shyvana is always being ready to take the farm off a laner when they recall to base.
More accurately, you can only play Shyvana if you have the encyclopaedic knowledge of junglers necessary to counter-gank effectively, since your ganks pre-6 are garbage and having
no map presence pre-6 is
not an option against any half-ass team. The problem is, that's not why people play her. They don't play her to out-duel, counter-gank, or invade.
They play her because she's strong top and they think they can just putz around the jungle farming wolves and wraiths, show up at 30 minutes with a Golem Spirit and maybe a Sunfire Cape and somehow have the same presence as a top lane Shyvana with a BotRK/Hydra, Sunfire, and Randuin's.
To the 1 out of every 100 Shyvana players who actually counter-jungles, counter-ganks, and generally has an actual impact on the game other than to show up at the team fight stage with barely more gold than the support, you have my respect and best wishes. To the other 99, just play Aatrox or something if you want to "carry jungle".
She's in a bad solo queue place. That's what I think anyway.
Her top lane is fantastic. She trades well, wins duels, and escapes ganks easily. Her power spikes more with three items than anyone except maybe Jax. She can split-push late game with relative safety thanks to Burnout + Dragon's Descent, and she never really "falls off" in team fights the way many bruisers do.
The problem is that all those things require items, which require gold. You
cannot, mathematically, get far enough ahead on gold to manage that farming only jungle minions. You need kills, and you're pretty much reliant on counter-ganks for kills since you aren't going to be ganking successfully very often.
This can and probably will change in Season 4, but right now if you're playing Shyvana to be a herbivore jungler - just stop, please. If you really want to play PvE from 1-6 and gank every four minutes afterwards, play Nocturne or Amumu.