Shyvana's only problem is that she is a frontliner/off-tank without CC. Her only CC is her ultimate, which is an unreliable and bugged knockup (bugged because sometimes the knockup doesn't happen due to the wonky hitbox from her ultimate). Because of this, she isn't good as a peeler, which is what most people want tanks and bruisers doing. She is better at diving and going for the enemy carries, and killing them. She is all about surviving to do damage.
That is maybe the reason why many people criticize her. She is not a bad champion, it is just that champions like Sejuani, Gragas, Nautilus, Zac, Nunu, Rek'Sai, Vi, and even assassins such as Ekko and Fizz have much better initiation potential, and they also have more reliable CC, which can allow them to peel for their teammates. Even champions considered to be weak such as Darius, are better than Shyvana at peeling and CCing teammates (although Darius has inferior intiation potential when compared to Shyvana).
You don't need to be afraid of what others think when you pick Shyvana, but please consider that she has an extremely unreliable hard CC and has no peeling potential. Sometimes it may be better to pick another tank/bruiser. Shyvana's advantages are the fact that she has one of the best damage potential out of all tanks and bruisers, and unlike champions such as Darius, she is difficult to kite, due to her mobility. If you have other champions at your team that can compensate for her weakness - I like to combo her with Lulu, for example, as Lulu has hard CC and makes Shyvana even easier to kill AND kite, with her abilities, other good champions to pair with Shyvana are Orianna, Amumu, Morgana, Fiddlesticks, Diana, Cho'Gath, Lissandra, and many others - then it may be a very good idea to pick Shyvana.
