1. Forgetting to balance enchantments.
You have your two-handed weapon, 1h weapon & shield and dual wielding 1h weapons options. Which ones ill you go for? In most CRPG's you'd go for the last two. Why?
Because the designers seem to forget that TWO magical items equals TWICE the magical enchantments, hence why such combos are almost always vastly superior to a 2h weapon.
You have a paralisis enchantment on that big 2H axe? That's nice, I got a paralisyis enchantment on my 1h sword and a blindness enchantment on my 1h mace. I deal 2(3?) damage types and have twice the chance to incapacitate you.
What's that? But you do more damage 2d6 +5 fire damage? Not bad. I do 1d8+5 fire and 1d6+5 ice damage. Opps. Looks like you underperform there too.
2. Loot/magic obsession.
Finding loot is part of a CRPG charm. But it's not waht a CRPG should be about. It's not why we remember great fnatasy stories. Your average CRPG protagonists goes trough magical items faster than a starving man trough food. Magical items constantly discarded, used for 5 minutes untill a better weapon comes along.
Long before the end of the game, every single inventory slot is filled with magical items. By the end, a character would cause a magic detector to explode. She sheer magniute of magical energy radiated over the hoards of legendary/epic items that the world hasn't seen in millenia would be OVER 9000!!!
Magic and magical items are overused. When everything is magical, nothing is. Magic itself loses part of it's charm and "oomph". Powerful magical items are ntohing but trinkets to be discarded.
When you think of Aragorn - was every single thing he carried magical? Did it have to be? Do characters in fantasy storeis switch equipment every 5 minutes? No, they find something nice and stick with it.
It's one of the reasons I loved BG1 atmosphere so much. It felt so real. A qualtiy steel weapon was viable even at end game. You didn't finish the game with everything being a magical +5,+10 uber-item.
3. if less is more, more is less?
Padding the game length with unnecessary, repettiive fight. Every road will have bandits. Or hostile wildlife with no sense of self-perserveation. And they will respawn.
Sometimes entire game sections will be nothing more than padding (looking at you FF) /fillers.
Because clearly, long game = automaticly better game. Right? Right?