So rather than give general advice I guess I can post a "build" that might illustrate some things and also be an interesting middle ground between caster and melee. I can't promise this build works well in Ultimate but it works fine in Veteran.
So this is a Commando (Demo/Soldier build) I call this the Killing Ground build.
This is my tentative GrimCalc build:
http://grimcalc.com/build/LdXiFj
My current guy at level 45 has 170% cast speed. His weapon is the Kymon's lightning scepter and shield is Elementium. The weapon has Blessed Steel for the res reduction (this replaces manticore devotion since the two won't stack).
Baiscally Stun Jacks is your main source of damage. Put Arcane Bomb on Flashbang and put Assassin Mark on stun jacks (I think my link might not show that devotion). Since stun jacks hits so many times and does DoT's even modest OA with Flashbang can proc crits (FB is a huge DA debuff and therefore OA buff).
The way this fight is mostly mid to close range. You start off machine gunning FB at things from long range to proc arcane bomb and make em all confused. When you want to kill something fast put Thermite close to them then Blitz and blessed steel then throw stun jacks right in their face, refreshed Arcane bomb when needed. For bosses use Overguard to stay alive and defense devotions should help as well. Also you can move between close and mid range and still stun jacks things and thereby avoid really hard hitting moves. This should result in something like -60% or more lighting res reduction and about 30 or so -physical res which help this physical hit and the internal trauma dot. Thus you wind up with a huge "Killing ground" of mines, flashbang flahes, and tons of stun jacks. This also works really well for Elementalists with Grapsong vines + mines + flashbang (AB on vines in stead is superior to on FB) but you would use something else for main damage (storm totem, savagery, primal strike, fire strik etc). Arguably a better killing ground with Elementalist since Vines is a massive slow with points and procs Arcane Bomb amazingly well. The main point here though is as a Commando you get the shield with overguard etc etc to deal with bosses/heroes which are not really gonna stay CC'd well. Elementalist should be able to do ok, but it won't be as obvious how to layer everything to a new player.
This build takes a lot of energy, but its ability to joust in and out is very nice and useful. Plus Blast shield with menhir's will allows you to deal with spikes in damage with out needing to panic or flat out run. On the other hand its need for energy can put a dent in your armor rating if you don't. It also can allow you try out offensive or defense devotions depending which tree you go (but I would say rushing Arcane bomb is best).
Its a fairly good learning build as you can 1) see difference between melee and not-melee 2) you can see how CC helps and doesn't help (i.e. FB rocks normal large spawns but is just the fumble for bosses) 3) you can see the effect of one the better remedies for melee, i.e. using a shield
Also I am thinking of adding significant retaliation to this build but that takes itemization and isn't somehting for new players really but its an option. There are a lot of tweaks this build can have for example taking one point in canister with 3 in transmuter is a massive stun, but I just use flashbang. This build is on the edge of just enough things to do, adding more probably takes DPS away from stun jacks spams.
Stun Jacks itself is a rather interesing and versatile power. Although probably no longer straight up hugely damage like it once was and the energy cost is substanital with high cast speed.
