So let me start out by saying that Tales of Maj'Eyal is probably one of the best RPG/Roguelikes I have ever played, hands down.
For the TL;DR people: The game is amazing, but completing it on normal difficulty will take hundreds of hours because end-game balance is too dependent on early-game character development. The game becomes unwinnable 30 hours before you realize it. For the rest of us: Keep reading, and I think you will understand.
ToME has 26 classes at the time of this writing, all of which feel and play very differently. Like most RPGs, skill points are gained upon leveling and can be used for both active and passive effects. The skills for each class are unique and allow players to develop their own playstyles, though generally each class has its own style of combat and a playstyle that rewards sticking to their class-specific strengths. Summoners draw hordes of creatures to overwhelm opponents, archmages channel elements to great effect over an area, and rogues set traps and use stealth to outmaneuver or outwit opponents. There are even more creative classes in here, like a time warden (or time mage) that specializes in temporal effects and paradoxes.
The world has tons of surprises and interesting levels/areas to explore, acceptable story and interaction (for an old-school roguelike) and though nothing ever changes, the vast variety of mechanics assured that the game did not get old for me after 90 hours of gameplay, and likely would not for another 90 hours.
But Tales of Maj'Eyal does commit one assault upon the unwritten laws of successful developers, which is a learning curve that feels more like a cliff than a slope.
The tutorial explains a little of the game's mechanics, but understanding is better gained by blundering through the world and slowly learning what each of the many confusing formulas and statistics mean, and how important they are to the core gameplay. It takes dedication to keep coming back when mountains of unknown skills and abilities assail you from every side, and through trial-and-error, learn to slowly overcome that mountain. And believe-it-or-not, I actually enjoyed the game very much once I crossed the barrier between hopeless bungler and still-hopeless-but-educated noob.
The true problem with the game is that it can become unwinnable very early on, and the players will never even know. The may even feel overpowered for a while, as they make one-strike KOs against hordes of enemies and pass tens of dungeons without a serious challenge in any of them. Then suddenly, a rare varient, a beligerant abomination of a boss-class monstrosity strikes, and they find themselves hopelessly outmatched, their only recourse to grind for levels.
This is the summation: even with permadeath turned off, you can make a mistake in your character build early on and not realize that your character is doomed until late-game, when you have already invested thirty-or-more hours into their development. So you will tragically blunder on, dying every few floors until you finally realize that your goal is impossible and you must start the game over again from the beginning. Worse, if you play with limited or full permadeath (as I did), you may be destroyed by rare variants before the game is even supposed to become difficult again.
Compounding this issue is the fact that there is no way to carry multiple saves in this game. You cannot save before making a major decision and restore if your decision was wrong, and copying the save files in and out does not remove this problem. You save upon entering a dungeon, entering the worldmap, or dying, so saving often is required as reloading will often be the only way to escape an impossible situation.
If the game were balanced so that a non-ideal build could still win the game, or ideal builds were easier to achieve, or at least saving to multiple save files was allowed, I would recommend Tales of Maj'Eyal as it is an interesting game that supports a wide variety of skill sets and play styles. But because of the intense difficulty and the almost impossible foresight required to win the game, it sits still-unfinished in my library and will likely remain that way for many days to come. A good game, but not recommended to anyone without weeks to burn away and incredible patience for doing so.
*Full disclosure here - I played the game on 'normal' difficulty for every playthrough. There is an easier difficulty that decreases the monsters' strength/abilities by 30%, but it does not give classes, races or achievements and so it does not appeal to those like me who want to feel they are accomplishing something while playing.