All right, there hasn't been a post here in a while so, I thought I'd go with something a number of other forums have discussed before.
3 biggest disappointments of the 4th generation and why.
mine would have to be (entirely in reference to standard competitive play),
With the advent of trick room, He had such high potential as a trick room sweeper. Unfortunetly, it's become pretty easy to predict and switch into his only stab. Latias was the beginning of the fall for me. When you only get three trick room turns to do damage, he really needs to use all of them well. Even if you predict latias, he can't come close to the OHKO he needs with Stone Edge, assuming you even make contact. He's just quite predictable and doesn't have the typing complement to his respectable defenses to reliably stay in outside of trick room. A trick room sweeper generally wants to operate pretty straight forward. When you find yourself having to make pinpoint predictions on every single move, you better be right much more often then you are wrong, or life is going to be testy.
Great potential coverage on the physical sweeper set. Great ability at face value. But his movepool lacks the physical-based power to use it effectively, even if he gets a motor drive boost. His base speed is wanting, resulting in a general trend of losing out to other, faster options. He lacks the necessary bulk/defenses + typing to make up for his flaws.
It's been said once, it'll be said again, Scizor + Bullet Punch = Usage Death.