There's a lot I could say about ADOM but I'll try to keep this brief:

Positives
- The fact that the base ASCII game is, and always will be, free (it's included in the Steam version, but you can download it stand-alone from the official website)
- The new graphics update makes it much easier to see what's going on and control your movements compared to the base game (i.e. if a monster is hostile to you, health bars, dots above sprites denoting status effects, the ability to click on things is especially helpful in your inventory,
- The game has absolutely incredible depth, which the most recent updates have added to with new quests, monsters, items, locations, etc. ADOM has always been a huge game, and continues to grow even bigger.
- Speaking of depth, the combat system, with different tactics settings and multiple approaches to attack, defence, and fleeing, is great
- The most depth in any game I've ever played. Seriously. It's hard to learn, almost impossible to master,
- The fact that the dev(s) are still updating and maintaining this game AFTER TWENTY-FOUR YEARS (seriously, it came out in 1994, you can look it up. I've been playing this game on-and-off for about 13 years and I'm STILL learning new things!)
- Good music
- Funny little easter eggs hidden throughout the game

Neutral
- Probably the steepest learning curve you'll ever encounter in a game that isn't Dwarf Fortress
- You will absolutely need to read a guide/wiki while playing ADOM. This is not a good game to go into blind.

Negatives
- I dunno man, you might not like it?

ADOM is easily in my Top 5 Games of All Time. I have 283 hours in-game on steam, but if you count how much I played as a kid I should easily be over 600, maybe a few hundred more. That's amazing bang for your buck.

All in all, if this seems like a game you'd enjoy, $17 CAD is a steal.

Note: For any new players or people who want more info on the game, I would recommend the following resources:

The Improved ADOM Guidebook
http://igb.epizy.com/toc.html?i=1

Although it is no longer completely up-to-date, I'd say it still has about 95% of the game's content covered and is a great way to learn both basic and advanced game concepts.

The ADOM Wiki
http://ancardia.wikia.com/wiki/ADOM_Wiki

Not as simple as the Guidebook, but includes an easy-to-use search function and is up-to-date.