That depends on what you like... the games are indie RPGs with a very oldschool aesthetic. The closest comparison, mechanically speaking, is probably the earlier Ultima games. I liked the Avernum games a lot (only played 1-4 so far though) because I think they have really great writing. Set in massive underground caverns that act as a prison for the empire of the surface world, the games really create a believable subterranean society of outcasts, and provide plenty of opportunities for old-school, party-based adventuring. I originally played the free demo of the first game back when it was shareware being sold on the author's website, and was hooked by the end of the demo and ended up buying the original trilogy (games 1-3).

The interface leaves something to be desired, though, and the graphics are very simple. And you'll be reading lots of text. If you don't mind that, however, you should definitely try them out -- you may find you like them a lot!

Note that there was an engine and design upgrade that came along with Avernum 4, so games 4-6 are a LITTLE more user-friendly. The first 3 are very old, and it's noticeable. You could start with any game in the pack, really, although personally I always like to go in order. But they are relatively separate form one another, simply taking place at different times in Avernum's history.

I'm at the end of Avernum 1, and I agree with everything Waltorious said. I had the game with a bundle, and it It took me a looong time to decide to play it, because of the graphics (I like oldschool pixelated stuff, but I really dislike the sprites and portraits in Avernum 1) and the lack of direction at the beginning of the game (hint : head north). But now, I'm really enjoying the game.

Avernum feels strongly like the older Ultima games and its world of Brittania. A believable open world that you can explore at length, lots of stuff to do, good writing, interesting characters and the gameplay is decent. The interface is a little old and clunky, but once I memorized the main keyboard shortcuts, it was serviceable.
And I find that the idea of returning in the same underground world for the next games, like I did in Brittania when I played Ultima, is really compelling.

Get past the graphics and the old interface, and try it. If you get hooked like I did, you should have loooong hours of gameplay with it :)