He has a very weak midrange game and bad hitboxes on his normals. No good low pokes, no real range on any of his normals. Most of the moves you use to poke with have a ton of recovery, making him susceptible to jump ins, focus attacks or whiff punishes if you don't hit with them. Dudley just has a very hard time getting in against a good chunk of the cast.
He has bad defense, since his only invincible move is EX DP. His back dash is okay though.
He makes up with it by having the highest damaging and stun combos in the game, but you have to make sure you can hit them consistently or you'll end up in a bad situation.
Some of his target combos have a use (f. mk > mk > hp to break focus, st. lk > st mk as a frame trap, cr. lk > cr. mp > cr. hp as a low hitconfirm/OS for bigger characters) but a good portion of them are rather useless. They scale his combo damage a bunch (other than one) and can sometimes mess up your inputs when you're getting crossed up.
Overall, the character is still playable, you're just going to have to work harder than with other characters. If you aren't anti airing with him though everyone's just going to walk all over you like they did to me in Super.