Some thoughts now that I finished.
I ran an almost identical build as @IvanKaramazov
, and finished at level 136. Spellsword was definitely fun. I used a katana throughout, starting with Uchigatana ( I started as a Samurai to get that weapon) and later getting Moonveil, which i finished with. Great weapon, with a superb power. I too used the black knife set once I got it, because yes, it looks cool. Before that it was a patchwork of stuff that looked cool and let me roll.
I slung a lot of spells, and kept my flasks almost even / slightly skewed towards FP. For spells, I mostly used glintstone shard, and Loretta's bow for long range, which carried me far. Bosses and other big stuff got a steady diet of rocks, which wrecked them. Later I got stars of ruin, which I agree is a great spell. I also found the comet somewhat useless - it did help me cheese two bosses (the black assassin and the second to last boss when he's just standing there), but otherwise I never used it.
Tiche was the best summons. I used Luthel for most of the early/mid game (and she was great), and while I was excited to get the mimic, I never really took to it. I found its AI maddening, and no matter how I tweaked my loadout it stood around waaaay too much. I also liked the swordstress / night maiden puppets (or whatever their name is) - they were pretty aggressive and drew aggro, but Tiche is insane, just charging in constantly and almost soloing bosses. I will use her exclusively now.
As far as the game itself, it's 10/10, and easily in my top games of all time. The souls concept worked so well with the open world, and I'm looking forward to doing more exploring. The polish of this game is off the charts, and the fun factor is high.
Early game can be a bit of a grind because you are so weak, but that ends pretty quickly, and if you farm just a little bit (or heck, just explore), you can get "strong enough" fairly fast. Mid game, say from level 25 to around level 100, is an absolute joy. You always feel strong, but you can die easily too. It's also really fun to read about, say, the meteorite staff, and then go get it. I did this with countless items, seeds, flask upgrades, etc.
Endgame... once you get to the Giants and the areas that open up at that point, the difficulty ramps up. Those areas are challenging, and you start having to play grace site to grace site like you would in Dark Souls. I didn't care for the snowy areas much, but the fire giant was a fun fight, and Crumbling Farum Azula was pretty cool. Once I finished that I went straight back to the capital for the end bosses.
Now that I finished, I'll run around a bit and collect whatever bells I missed and tinker with respecing before starting NG+. Kind of wanting a big weapon/shield/faith build now.