Ken is one of the best "jack of all trades" characters in SF4. He has strong reversals, deadly knockdown tactics and one of the longest-ranged kara throws in the game. While characters that have lots of effective tools take a while to master, Ken is definitely worth the practice.
Ken's weaknesses are his walk speed, the lack of range on his Focus Attack and his extremely poor backdash. His Ultras are either weak in combos or tough to land. These weaknesses are not very substantial, but they're enough to be a hindrance.
• Strengths •
+ Has a strong anti-air game.
+ Reversal game is reliable with a shoryuken that cannot be safe jumped naturally.
+ Combos carry opponent to the corner quickly.
+ Can combo into sweep for a knockdown game.
+ A great crossup game along with an overhead.
+ Can build meter quickly with all of his special moves.
+ Incredible range on his kara throw.
• Weaknesses •
- Fireball has slower than average recovery.
- Slow anti-projectile attacks.
- Walkspeed is slower than average.
- Short range on a very slow backdash.
- Can't rely on Ultra combos as tools.