Well, for sure, the levels and world contribute significantly to the game being boring. On the character front, however -- it's been a while since I played it but I don't think that necessarily more character abilities = better. The abilities in the game felt extremely MMO-esque. Like, "hit the enemy for 110% dmg and have a 15% chance to stun" and then when you level up you can spend a point and it becomes 111% dmg and 16% chance to stun. The ability offered me basically zero tactical decision-making. Basically, if I was fighting someone tough, I used it on them every time the cooldown was over. In other words, dump points into a few abilities and then just use them every time the cooldown ends. Yawn.
Things have improved a bit in this regard since you played it. Most classes seem to have a core of specialized abilities with specific tactical uses and not many of them are based on low percentage procs. For example, the berzerker (a simpler class) has a stun (it tries to stun 100% of the time), an AOE, a move that instantly charges a few spaces and tries to daze the opponent, an AOE warshout that tries to confuse enemies in a frontal cone, an expensive attack that tries to kill enemies below a certain HP percentage, etc.
There are also a few less specialized abilities (sunder armour etc) that mostly serve as extra damage, but you have to be careful not to run out of stamina so you won't want always want to spam them every time they're off cooldown.
It is true that you will probably develop a set routine for most fights, but things get interesting in the dangerous situations.
For DC:SS, for example, a melee fighter's tactical choices revolve around world positioning (Tome's world is a random mess of trees... at least the beginning) and using items intelligently. Again, I have a hard time remembering but I'm pretty sure the items I found were mostly useless and/or boring enough to forget them.
The levels using the "random mishmash of trees" layout are rare. They're less horrible to deal with now that we have autoexplore.
Potions and scrolls were replaced with infusions and runes. These provide healing, curing, speed boosts, teleports and other effects, but aren't consumable. They're on a timer, so dealing with a tough fight requires watching your cooldowns closely. Wands and equippable items with useable effects also exist.
So most characters have a lot of choices regarding what move to make in a given situation.
However, the game is less tightly balanced than Crawl, so there are a lot of easy fights where your choice doesn't matter and a few extremely dangerous fights where the best play is to run away. That's more of a pacing problem than a character system problem.