Everything that is RPG.
First impressions. Awesome soundtrack (correction: fucking awesome), like the atmospheric rock feel, not medieval or fantasy-like which is great for me. The game in general feels solid and responsive. Not so sure about the colored balls (health and mana indicators) in the corners, they kind of pull you out of the experience a little (maybe it would have blended in a bit better if the blood was darker (more like, err, blood?). Enemies are very easy to kill to start with, which is refreshing as I was expecting a grind, though it probably would get boring after a while if the entire game was that easy. The textures seem to wobble in some places (probably because of the way pixel aliasing is used), which might give you a bit of a headache after a while -- I think that weird rendering issues can break the illusion. After a while you get used to it and it goes away (it helps if you focus on the cursor), but every time you get drawn back out of the game (e.g. when your focus changes to the UI) you notice it again which is irritating.
Enemies. I like how if there are a horde of enemies, some of them run away when you kill others in quick succession -- makes you feel powerful. It’s pretty neat how special enemies can revive other enemies, so you have to kill every last one to kill an entire horde. It’s great when they drop gold! I love gold! Frequent small rewards are a must. I haven’t quite figured out whether or not it’s important that enemies randomly do not drop stuff (if they reliably did, would it make you want to kill them more?). Very hard enemies drop a lot of healing potions, which is awesome.
Stats. I read that stats are important, as it lets the player know how they’re doing (some argue though that this could pull you out of the game illusion)... I think it often draws me back out when I see the nagging “new stats” icon that pops up, not sure how I feel about that button -- it’s good because it tells you when you can improve your character, but maybe how fallout does it is a bit nicer (only when you level up). I often don’t care so much about XP, just health and stuff to collect (maybe that’s my inner FPS-addict speaking). I didn’t notice the progress bar at first, and I think that’s because it blends in too well (you have to hover over it, which might not be so bad). I prefer how fallout does it, when you gain XP, it briefly shows you the XP progress bar.
Objectives. Gets slightly boring when you can’t find your way to the next objective or enemy, Fallout has an indicator system which solves this very nicely... does anyone actually enjoy treasure hunts, where you’re blindly going from room to room? I think treasure hunts are only fun if you have to use your intelligence to find stuff. (Correction: I just discovered the auto map, nice feature, seems to blend in quite nicely and the icons are really neat.) I don’t like tutorials, but something early in the game that would have guided me toward the mini panel would be nice... maybe if something had encouraged me to play with stuff on the UI, or maybe made the mini panel button more obvious.
NPCs. Interacting with friendlies if you could speed up conversations some how. I tend to just scan for bits of important information... I’m less concerned with the story.
Conclusion. Very addictive and solid gameplay, but can be mentally taxing as there is so much to remember (but this is typical for any RPG).