Party:
Eder: Main Tank (all but invincible)
Crom: Custom Barbarian (decent damage dealer and half-assed tank)
Valaria: Custom Druid (not terribly formidable, but I like Woodskin and stuff)
Mia: Custom Priest (fantastic buffer/healer)
Kana: Chanter (great for buffing ranged reload speeds)
Lond: My main - Rogue (best single-target damage dealer)
9 out of 10 fights:
Position my tanks - block passage to the rest of the party.
Slaughter everything with (mostly) the rest of the party, all using guns buffed by Kana.
Heal and buff when doing tougher fights.
I use, literally, none of my active powers except spells and Rage for my Barbarian. At least, it's extremely rare - as they're just not needed. I've never used a single potion or any kind of food.
I'm playing on Hard - and I'm not finding much in the way of challenge anymore. But that's fine, as I don't really enjoy the micromanagment of the combat system.
It's more or less like Baldur's Gate when it comes to "Core" challenge level, except the "hard" fights are much easier, so far. It starts out very hard - much like BG did, and starts to get easy around level 4-5, which is also much like BG. But BG hard fights were often REALLY hard - mostly because of nasty spell casters, where PoE doesn't seem to have many of those, at least not in my ~35-40 hours of playtime. The only fights I've had trouble with - with my current setup - were the Shade fights in the Lighthouse - until I found a decent bottleneck and I started using my Priest properly.
The combat system doesn't seem very well balanced in terms of challenge curve. I think most of their mechanics are relatively sound in concept (but really quite dull) - they just need a few more releases to hit a sweet spot. Perhaps the second expansion will have a better challenge curve.