ya, he's squishy. The idea with Nightcrawler is to not get hit--good thing he has tons of teleports and dodge. I put agile strike on main attack left click, and his starter teleport (only ever put 1 point into this) on right mouse button. This way, you can easily dance around your target as you mele them.
Main play style for me is to lay down an Infernal Brimstone field, and Flash and Grab everythign into it. If you see it on your screen, no matter where it is, and cna be grabbed and pulled to where you are. Collect all the people's in your little basket and kill them. F&G i also a stun, as well as a Great DoT inside of IB, so consider that ample time to smack on things while they can't hit you. You can also use F&G as a ranged single target, as you keep distance and telport across the screen to avoid anything you need to. It's an amazing skill.
Blink strike is great for leveling, but it's not very good end game--it is terribly for single targets, great with 2-3 targets, and horrible with about 5 targets, despite what it sounds like. It's a fun skill, but not nearly as good as F&G. consider leveling with it, though, and with Agile Strike as your spirit replenisher. YOu also want to max Heartseeker guard in the sword tree, and One Step Ahead--I think in the teleport tree. X-Slash is his best DPS skill, probably (if you are using his excalibur unique sword in the 1 slot), but is very spendy on the spirit. Not easy to level with it. Brimstone Beatdown is a really good skill that comes very close to X-Slash in DPS, but it has terrible camera bugs--just hold it down and use it enough, you'll see what I mean. But, it's pretty cheap and is close to X-Slash, so it's a decent option.
Unfortunately, most of the stealth mechanics in the game are currently broken (you will just pop out for no reason), so skills like Bamf Bomb aren't that great right now. Still, a skill like Obscuring Brimstone is very helpful for the crit buff, or escaping bullseye's targeting. same with his starter stealth skill, which only needs one point.
Focus on HP, defense, and dodge when you are gearing if you have death problems. You want those to be pretty high, anyway.