ZDoom

1. That is intentional because otherwise it would look like shit
2. That's a limitation of the software renderer's fog handling and not a bug
3 is a mappin bug. The Ultimate Doomer is (in)famous for an extremely high threshold for rendering glitches and many of his maps show such problems if you look closely.

Some bugs I've seen..

The pics are from E4M5:

The green glow/fog extends too far:
[url=http://img464.imageshack.us/my.php?image=doom00004hr.png][img]http://img464.imageshack.us/img464/9459/doom00004hr.th.png[/img][/url]
Normally, this green "fog" or whatever shouldn't extend pass the door.. since when you go through the door.. it is non-existant..

The area around you should be "within the fog":
[url=http://img464.imageshack.us/my.php?image=doom00012yr.png][img]http://img464.imageshack.us/img464/4537/doom00012yr.th.png[/img][/url]
It's hard to explain.... but basically when you enter near the doorway, the the area should be foggy.. except for whatever the reason, the area around you between door and the main area doesn't seem to be affected. It's hard to explain what it "should" look like.. but the "more correct" looking output should be something similar as to what is shown in GZDoom...

Hall of mirror effect when standing through the door:
[url=http://img464.imageshack.us/my.php?image=doom00027db.png][img]http://img464.imageshack.us/img464/614/doom00027db.th.png[/img][/url]
In the area near the big huge door, there is a door (that requires the green key) that leads to some ammo... standing in the door, you can easily create the hall of mirror effect...