Good places for ideas. Dwarf Fortress is pretty much the ultimate in procedural sandbox. It's also a good way to learn about how stuff gets made, why certain metals are better than others, etc. It's a cool low (really, no) magic fantasy setting. You could even use a screenprinted large map as a campaign world. (Not sure if you can print off the legends/history, but I think you can get to view it... so it should be printable as well. Huge, ready-made backstory if you ever wanted it or needed it.)
I really liked Ultima5's virtues system. I've always felt like there was something missing from the WAY people played fantasy RPGs. Ultima5 also squeezed an incredible amount of atmosphere out of very tight computing ability. The reagent system is kinda cool, too, I've always liked the free-form magic system. (Seems like spell components are always the first thing that gets chucked from D&D 3.x games, in my experience.)
NetHack is a great analog for "you're going to die. A lot. but it will be fun." DF has that as well.
Just some thoughts that I had, while I'm waiting on my book to arrive in the mail.
Hamun Ry (Wiz 4)
Str 10 Agi 15 (+1) Sta 11 Per 11 Int 17 (+2) Luc 10 (Unholy House). Align: C. AC: 14. HP: 13. Melee +1, Ranged +2. Crit: d8, I. Save: Ref +5, Fort +3, Will +4.
Spells: 1: Choking Cloud, Comprehend Languages, Detect Magic (odd crystal growths), Magic Missile (mirror images), Runic Alphabet (Mortal) (ravenously hungry), Ventriloquism (rain of frogs)
2: Detect Invisible, Levitate (extremely difficult, d14), Mirror Image (20% chance to raise/lower luck by 1d3 points).
Equip: Ring of the Sand Djinn: +2 AC/saves, Invisibility for 1min/spellburn point, or unmake for great, unknown effect. Padded Armor, Longsword, Longbow, quiver w/20 steel-tipped arrows, 10 silver-tipped arrows, backpack, spellbook, quill and ink, sturdy parchment (10 sheets), 5 days rations, high leather boots, belt w/ belt pouch, gray robe, dark gray hooded cloak. Also carries 3 small mechanical toys: wind-up mouse, wooden puzzle cube, small jewelry box that plays a little tune.