250 seems to have changed the mesmer a lot.
Confusion is a condition that inflicts damage on each skill used. You can apply it using a scepter skill or the cry of frustration shatter. Backfire is a phantasm that hits target foe when using skills. The mesmer also has at least three skills that reflect projectiles to the attacker. The GW2 mesmer can thusly punish skill usage via hexes (phantasms, sorry), conditions, and reflection.
Denial of service
Imagined burden summons a phantasm that cripples foes. The mesmer also has an AoE skill that cripples foes and speed boosts allies. A greatsword skill knocks down foes in a cone ahead of you, ideal against those pesky melee fighters. The mesmer also has an array of skills to stun or daze or otherwise prevent foes from being useful (see above), with the bonus that these skills and conditions still have an effect if you cast it while a foe isn’t activating a skill. The shutdown mesmer is very much alive in GW2.