Been spending more time than I should have on this game (darn you DG, it's all your fault!

First point, this game is in desperate need of a manual. The tutorial provides a good start but doesn't cover the user interface fully, not does it offer proper detail on item descriptions (abbreviations, colour coding, etc). Even the basics like how to buy or sell items aren't covered (adding a shop in any new tutorial along with an NPC to interact with would help here) along with certain UI "oddities" (like having menus where the only way to exit is to click outside their dialog box). Yes, there is a wiki but that doesn't cover such details from a beginners perspective and is spoiler heavy. Just including some of the more informative forum posts in an HTML/text readme file could be a big benefit to beginners.
I did throughout gameplay receive several donation solicitations - since I was playing the "paid for" GOG version these really shouldn't be present, though only a minor annoyance.
The item vault capacity is rather stingy in the GOG version (3 items only) - I'd suggest increasing it to 5 plus 5 for each expansion.
UI:
- the bottom toolbar needs more capacity - 60 items may seem plenty but given that many items take a slot and some talents multiple ones (e.g. chants and hymns use 3) it's easily filled at medium-to-high levels (I have been able to boost this to 108 via lua editing). An option to sort the items (by class, type - activated, sustained or item - and name) would be a useful option.
- the right-click menu is handy but since it obscures the map tiles underneath, it makes it difficult to determine if a target is within range of a talent or not. To compensate for this, "out-of-range" talents should be grayed-out or shown in a different colour on the menu. Given how long this menu can get, having cascading sub-menus (by talent class, for example) would also be useful.
- the mini-map would benefit from a zoom function as resizing it currently doesn't change the size of area displayed.
- the pop-up at bottom-right is easy to overlook on a larger screen and can cover up a toolbar expanded to multiple rows. I'd suggest placing this at an offset to the current cursor position.
- the "show known lore" option should give the option to view individual items full-screen (as displayed when you first encounter them) when you double-click on an item. The current setup (details displayed in the right-half of the screen) makes it harder to read longer items, like the Spellblaize Chronicles.
- selecting items by letter in the inventory screen doesn't work (though there seems to be a mod that fixes this).
- when playing the Adventurer class, selecting the "Wordly Knowledge" prodigy results in a blank menu you can't exit from (yes, there's no point in choosing this, but the prodigy should become unselectable instead).
- the message log can get very busy in crowded areas (especially with skills like Precognition and creatures like luminous and radiant horrors) - some (configurable) means of filtering out distant events (which could then be viewed in the full screen log display) would be useful. Another option would be hotkeys that jump forward/backwards to lines that directly affect the player (skipping NPC-on-NPC events).
- the economy needs more balancing with regard to item prices. By the time your character is able to afford anything in the shops, they will be finding better loot in the dungeons. I would suggest halving shop prices and allowing "compatible" characters (matching races like shalore/ogres in Elvala or halfings in Derth) to haggle to lower prices further ("unusual" character classes/races like Drem or Cursed may conversely face higher prices due to merchants' reluctance to deal).
- hard level limits (50 here) are my least favourite game mechanic - with the expansions it is all too easy to reach level 50 well before the end of the game. If there is a limit imposed, it should be one which players have little chance of reaching. Yes, this can be removed with a mod but that mod requires you to start over.
- there seems to be very little "character" about the towns and almost no point in visiting them after the initial stages of the game (thanks to the Transmogrification Chest which removes the need to visit towns to sell loot). This seems a shame since ideally towns should provide a change of pace after a heavy dungeon bashing session. To improve matters I would suggest:
- all NPCs should have talk lines relevant to the town - this could be local gossip ("Did you see the last festival the Ogres arranged in Elvara?") with the occasional pointer to a new quest (as currently happens after the defeat of the Master in Dreadfell). A nice touch would be to add lines as the player progresses in their quests ("Did you hear that some crazy witch was found in our graveyard? What is the world coming to?").
- add a tavern to towns where players could pick up rumours (some even true), gamble for gold or items (a good way to introduce new magic items before the Last Hope 4,000-gold merchant comes into play) and maybe pick up simple quests (a lost treasure map that opens up a new location to explore, item delivery or escort quests, etc). Since taverns are referred to in one of the lore items, it seems odd not to have any.
- given the vast array of possible item powers, it is frustratingly frequent to find an item that provides really good bonuses in one area but insufficient ones elsewhere. Having the ability to "customise" an item (possible only with gems currently) or combine two items with a chance of getting joint bonuses (or the complete loss of both items in a spectacular fireball) would be useful and could provide a long-term use for the alchemists (this could tie in with their quest since each could have a different item specialty when they join the guild).
- Save game size: My current character has a savegame size of 180MB, even though most of the files are zipped (using RAR reduces this to 130MB). Not a big issue with a single game but those with multiple characters (and regular backups of savegames need to be taken in my experience, since sometimes areas aren't saved properly) would benefit from seing this reduced. The biggest cause is "once-off" levels like the tentacle tree swallows or the subvaults in High Peaks. Since these cannot be revisited (the vaults can but only during the current High Peaks level), a simple fix could to be to just delete them once the player leaves.
- I encountered some game-breaking bugs (in particular, critical NPCs vanishing) due to areas not being saved properly (the data would be in a .tmp file rather than a .teaz). This was quite rare but the symptoms seem to have been reported in other threads here, so it may be more than a system-specific issue at my end.