Every class but Templars have a unique gap close you can get from weapons or any skill tree other then that class, other then templars.
Dragonknight - You pull the enemy towards you, this is absolutely amazing because you could be pulling the enemy to your group or pull them from stealth to a spot they don't expect (could be away from or out of sight of their allies). There are a few secrets DK's hide with this ability that make it amazing.
Nightblade - You teleport to your target,If you time it right you can go through objects to targets, you even ignore all possible hazards that lay between you and your target (daedric mines, Caltrops, Lava rune, etc). Not only is it extremely useful, but Its the only Gap closer in the game that uses the Y axis. When I play on my nightblade I love going below a cliff and jumping up to my target, when if i was using invasion my person would go into the animation for a second then come out of it because i cant charge up there.
Sorcer - Bolt Escape, This is not only a gap closer, but a disengage, it also doesn't even require a target. Without Bolt Escape Sorcerers wouldn't even be considered as a mobile class.You can use it to traverse obstacles and get to tons of areas in the world that no other class can get to (Unless a DK pulls himself to you, or a Nightblade jumps onto you). Its probably one of the most fun abilities along with one of the most useful abilities in the game.
Templar- Nothing really special about this other then the look, you charge on the ground and can either do AoE damage or interrupt targets similar to Invasion/Critical charge. This ability even has a GCD (Global Cool down- After you cast it , you character sits there for a bit and you can do anything, including casting other abilities) and the damage is lacking a fair bit, its better to go with invasion even if your a magicka build.
Every class has signature abilities. I personally love Chains, BE, and Teleport Strike, but Templars focused charge is just lacking in every way possible. Which is why I hope ZoS has something planned for it in the near future, Hopefully a whole Ability remake for it (like they did with Blinding light->Radiant destruction)
~Thallen~