GeistSR: Nice
I do like Darkside quite a bit, minus the bonus postgame content that felt kind of empty.
To me, the "postgame" suffers from a few different issues:
* The game stops giving you gold; the Dragon Tower is the last location to have a significant amount of money. This means that, for example, you are unable to level up your characters because you can't afford it (cost of gaining a level scales quadratically, while the XP required for a level up doesn't scale past a certain point that you are well past at this point). This has the result of making XP useless.
* Even worse, one of the postgame dungeons requires that you pay millions of gold in protection money, or else you have to go through traps that do absurd amounts of damage. If you try to train the levels you've earned, you're not going to be able to pay.
* The one feasible way to level up is with things that give you +X Levels (permanent), which are single-target, so the game ends up favoring leveling up a single character at the expense of everyone else. (If you have day of protection/sorcery items, then the Barbarian would be a good choice; have that high level Barbarian use the items, and cast Recharge Item if they run low.)
* Enemies are strong enough that you basically need Day of Protection to do decent damage, and since that only boosts physical attacks, offensive spells (excluding Mass Distortion, which is a cleric spell, so the sorcerer still doesn't get to do much) are basically useless at this point. You get to the point where a sorcerer does more damage with an obsidian dagger than with a powerful spell.
* AC also becomes a problem, as the core mechanic of having to roll a fixed size die to hit AC doesn't scale well. (D&D and d20 system games have this issue, especially if you're running 3.0's Epic Level rules.) Furthernmore, the only enemies that target AC and are of any threat at this point preferentially target your Cleric, so as a result it's only worth boosting your Cleric's AC, and only for that one dungeon; otherwise, armor is essentially useless. (Worth noting that enemies using magic attacks elsewhere in the game makes AC less useful than you'd expect, and when combined with the fact that all equipped armor breaks (not just the torso armor, unlike MM3) once you reach -10 HP, it just becomes not worth bothering with armor.
I do recommend doing Dragon Tower, especially with that one minotaur dungeon being a real pain if you do it before that tower, simply because it does give you nice rewards (especially if you go there early), but after that, the later part of the "postgame" just doesn't give you enough rewards for it to stay interesting.