Nox is a game from 2000, quite similar to Diablo. One of last games made by Westwoood before EA sucked the blood out of it.

Nox had many great ideas which were lost with it. A lot can be learned from it. While there's no substitute for playing it*, some things can be observed from gameplay videos.

*(Single Player campaign is long, and each of 3 classes has some levels available [b]unique[/b] to that class. No random generation. Huge monster and spell variety, except for warrior who has 5 skills).

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video1 (from Dynamic Light thread) shows interesting field of view, and multiplayer action (Warrior  vs Conjurer). Warrior uses 4 out of 5 his skills - berserker charge, battlecry, sneaking around, and harpoon. Conjurer uses some summons from single player (Mechanical Golem, Gargoyle, Trapper), lots of Force of Nature (the green ball), some crossbow, Blink, Slow, fireballs from a staff.

Trappers are interesting creatures unique to Conjurer. They self-destruct and have very low HP, but up to 3 spells can be put into them to create deadly combos. They're like mobile mines, but aren't invisible, and cost a lot of mana.

http://www.youtube.com/watch?v=KGbJvbDMEf8

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video2 (from Feedback thread) shows nice arrow trails in the beginning, otherwise is boring and the player is simply bad and cowardly.

http://www.youtube.com/watch?v=Om8IdqCZVoo

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video3 is again from multiplayer, Conjurer vs Warrior. A new spell not used in the other videos is Monty Python-esque Fist of Vengeance. The player used it quite well, when warrior's Berserker Charge missed.

This video also is very good for observing Field of View. One interesting detail is that vision is deliberately assymetric in some cases - windows are opaque if you're far away, and translucent if you're up close. This allows archers to ambush player. When stuff behind walls or corner is completely black, exploration is more exciting because you really don't know what's in there. In Diablo you could see a big room from far away even if doors are closed. A big room probably means a big fight. Here, you can't anticipate anything.

http://www.youtube.com/watch?v=iWx0HJsroto

One impressive kill in the beginning - Warrior was stuck blocking Force of Nature with a shield (it bounced back and forth). But Fist of Vengeance came from above !

Also interesting thing - levels can have multiple floors. You can see players using elevators.