I have to say, I'm really glad I've been playing this game with a friend instead of trying to do it solo. I played a couple solo missions and they were orders of magnitude less fun than cooperating. Especially since each class has different strengths.
Like, my Huntress can snipe enemies from a distance with her ranged weapons, turn invisible to sneak behind enemy lines, and set mines to blow up groups of enemies that step on them; however, she can't set up long-range towers or barricades, her crossbows are a single-target deal (mostly--there are some grenade launchers with a blast radius, and some triple crossbows that fire multiple shots at once), and she can't fight well in close quarters.
I've been playing with Miles, who has a Squire. The Squire is strong in melee combat, and can tank hits effectively with his strong defense. He gets access to all sorts of barricades, which can block off enemy movement, as well as a harpoon turret that can target enemies from a distance--good against flying baddies.
And there's also the Apprentice and the Monk, which I haven't seen much of yet, but they both have their own respective strengths and weaknesses. Plus even more in the DLC. So it's cool. Competitive balance.
The Huntress has five different traps, but I mostly find myself using the basic Proximity Mine because it's hard to go wrong with a big kaboom. It's the cheapest one, and it hits a group of enemies for a good chunk of damage. The other four are the Gas, Inferno, Darkness, and Ethereal traps. Gas paralyzes them, Inferno deals damage over time instead of a single concentrated blast, Darkness confuses and debuffs them, and Ethereal deals a HUGE chunk of damage but can only hit a single enemy. In most of the levels I've played so far, the Proximity Mine tends to just kill them in the initial blast, so not much point getting fancy, but I imagine that changes at Insane+ difficulties.