@ OP: I also like to play a battlemage or summoner mage in fantasy games.
I made my character to fit the idea and would've gone either way.
While my mage can do some damage with fireballs and such, his best ability is simply confusion.... half or more the enemies turn friendly for a few turns while my party kills the other half. :-3

I managed to find a few one use per day summon items too, so three of my guys can summon powerful things for boss battles, etc.

You could do worse than a sword and board Chanter with high might, high endurance and high resolve. I say, drop int - who needs to have a large casting range if you are to be in melee anyway? Just keep enough for the linger effect, but Int 20 will just net you 1 sec per effect anyway

You will have a very good deflection and your chants affect yourself, so you can drain life around you, boost your saves or reduce slashing and piercing damage with first level phrases. Second level phrases? Everyone enemy you is frightened, meaning lower speed and accuracy, or everyone in melee make the ground beneath them do frost damage - yes please! Level 3? Damage boost and deflection increase and burn and slash damage for everyone engaged with you.

And there are some very good invocations to throw in melee - summons to flank, and stun effects, and paralysis and charm? And that's not looking at level 3 invocations? All of average casting time. Not bad.

I would go the debuff route with maybe a moon godlike in order to be able to stay in melee longer and heal nearby allies?

Mooncurse: the cursed.. well cursing, moon... moonman. Yeah!

I think posts that use terms that are not defined while assuming everyone knows them are a bit amusing. Ie, the person that insists that there's a hard biological difference between wyvern and dragon and wurm, when they're all completely fictional and every fantasy story and game treat it differently. So here, "battlemage" is completely undefined. Are there two games which are not based on the same source material that agree what a battlemage is? I'm not sure. Does it mean a mage in armor, or a mage that joins the war instead of just making herbal supplements, or a mage focusing on destruction school of magic, or what? I don't need to know the answer, just pointing out that you can't assume everyone knows what you're talking about when fantasy terms are used.

Bethesda games have a specific class called "battlemage". Also, earlier D&D versions had specific ways for elves to swing swords, wear armor, and cast mage spells. I think this one is kinda standard.

I don't think a battlemage is a good idea in PoE, you'll just get a slow armored wizard that will die fast in melee.. There's no battlemage class, go for a Cleric, Druid or Chanter if you want a "balanced" combat/magic build.

I didn't say that spells are useless - but uninspired (mostly are copy pasted with higher damage or effects), and really tough fights are rare (at least on normal). Most of the combat is a slugfest through trash mobs and is there is no reason to waste spells or micromanage for these battles. I had to say by the end of the game I got pretty bored by the combat.

Disabling AoE spells are indeed powerful, but even in the final battle I didn't use much of these (since they didn't hit - I think only the trap like spells always hit when the enemy is over them), and strongest enemies fell under a hail of bullets

Yes, in Elder Scrolls series. But most people playing those games don't use the pre-mixed "classes. But several other games have something called Battlemage, and they are extremely different from TES Battlemages.

I named two battlemage examples that I thought were similar to what the op wanted to discuss. I did not mean to discuss how people play Bethesda games. Nor did I attempt to cover how "battlemage" might be defined by other developers, in ways that were not helpful to the op.

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Woot? You don't use spells. Normally I also use them seldom, but when I do they are well worth it. I killed the Adra Dragon like in 10 seconds. Got him prone, one mage cast some Minoletta 4th level, the other one a wall of force, Durance cast a pillar, and Grieving mother Disintegration. I did do some preparation - got him prone with Eder, cast the spell to weaken it and one priest to get the stats up (+protection from fear). I was like wtf.. especially since before that I tried like for 3 hours with a lvl 11 party and died. But returning at lvl 12 and preparing a bit better (to actually hit him - since the previous tries I didn't used protection from fear) almost felt too easy.

I suspect that ppl saying "spells are underpowered/useless" just don"t know how to use them ... I had a ton of laughs when my enemies were blinded+dazed+hobbled+prone+frightened, well were totally powerless thanks to a handful of 1st-3rd level spells !
Sure gunslinging is simpler, but as far as I've observed it's just good for a barrage when engaging, after that the firearms are so slow that they are'nt very effective.

To be fair on normal most fights are pretty easy without even casting higher level spells. I think the only real struggles I had was the Adra Dragon and the final fight... where I lost Eder and Aloth :(. Freaking AOE spells :/

I'm working on a wizard battle mage now @ level 6. I haven't really dared to tank but no problem going face to face as a 2nd line damage dealer if you are careful. Also, wizards just had their base and per level endurance raised slightly in patch 1.05.

Some suggestions I'd recommend are to have a hatchet (+5 deflection) and fine or better small shield (+12 deflection on a fine small shield with no accuracy penalty for small shield use) for when you are rushed or decide to go melee. Medium armor for the trade off between light & heavy armor cast speed limitations. Arcane Veil (+50 deflection for 10 secs) augmented with hardened arcane veil (+25 deflection) is also a must but you only get 2 per rest so use them appropriately. I imagine the build really takes off at level 9 & 11 when the per encounter spell use kicks in for levels 1 & 2 respectively. However earlier on you can cast level 1 Concelhaut's Parasitic Staff followed by level 3 Deleterious Alacrity of Motion for 30 seconds of +50% attack speed. Or cast DAoM and queue up some fireballs with the shift key for instantaneous nuclear annihilation.

For healing you can use level 2 Concelhaut's Corrosive Siphon. With high might you can get 60+ endurance over 10 seconds. It can be used at up to 5 meter range and comes with a small AoE for strategic placement. Combine this with Spirit of Decay utility talent for +20% corrode damage. Then there's level 3 Concelhaut's Draining Touch where you can get 40+ endurance instantly with the added bonus of 20 seconds of enemy weakness.

If you look there really are a lot of good battle mage spells for a wizard. Still though, there is improvement the devs can make to make it a bit more viable.

With the buffs defensive mage spells got in 1.05 a battlemage it's much stronger. Maybe the summoned weapons are worth it too, even though enchanted normal weapons have the advantage of the accuracy talent and.. well, permanency :)

If anyone tries a first line battlemage I'd like to hear their impressions. I still can't imagine how is better to use those spells for melee instead of nuking from the back. (I can't try on my own, PC problems...)

It depends how you play, I mean if you try to resist to rest after each battle, à la old-school, fights began to be hard when you have only 20% of spells/abilities and half HP .. Then hoarding some effective spells really help !
That's how I like it ;)

I also don't like to rest constantly, but 1-2 well placed AOE spells can turn the tide of many battles.
After the 9th level you can use your 1st level wizard spells per encounter. After the 11th the 2nd level ones also... And I finished the game without knowing this =)).
http://pillarsofeternity.gamepedia.com/Wizard