I've just finished the first two games. My times are:
Avernum: 64h
Avernum 2: 88h

Guess I'll be here a while :D

I have a tough time getting through these games. Not so much difficulty, but moreso the long time it takes to get through. Usually if the game is similar length to Baldurs Gate 1 and 2, I will mostlikely finish it. Is Avernum 4-6 the same as Avernum 1-3 in that aspect? I looked on how long to beat and it states that Avernum 4 is 60 hours while Avernum 5 and 6 and 39. That's a big difference and yet I somehow find it hard to believe.

I wanted to give Avernum 4 a chance to complete it, but don't want to spend a ridiculous amount of time to do so.

Spiderweb games are not for people that like shorter games. These are games that take considerable amounts of time to get through, especially if you take the time to really delve into them. If you are the kind of gamer that likes shorter games or gets bored quickly with games, just know going in that you might not enjoy these too much. That being said, there are a lot of games I get bored with after 10 or so hours, especially certain console games, but I can play Spiderweb Games for 50+ hours without ever getting bored. So just because you get bored with other games, doesn't mean you will necessarily get bored with these games. If story is important to you, then I would at least gives some of these games a shot.

Avadon is half the length of most Spiderweb games. So give it a go if you want something that's relatively brief. Avadon 2 will be released on October 30th, FYI.