The puzzles are fiendish and the combat is really tough. One of the puzzles in this game requires strength, so make one character VERY strong. Pressure plates can be stepped on to open doors etc. Otherwise you can spend your time walking around in circles like a madman. The flashing purple lights are teleporters - they transport you to some other location on the same level.
Portals are doors with strange symbols on both sides.
I used the cursor keys to move, Home and PgUp changes direction. You can use it to fight by picking up a weapon and clicking on an enemy - I prefer the latter way however. Open the E door first. Watch the pits, some have to be opened and closed with pressure plates. Get the key and other stuff and return to the 3 doors.