I finally completed BT 1-3 carrying a single party through the entire series! I played through using The Bard's Tale Trilogy remakes, so I posted most of my adventures in the thread devoted to the remake itself. However, this means I have now completed BT1-4 so I thought I would post something here as well.
My party for BT1-3
• Paladin
• Hunter -> Geomancer (BT3)
• Bard
• Rogue
• Conjurer -> Archmage (BT2) -> Chronomancer (BT3)
• Magician -> Archmage (BT2)
Here are my overall thoughts on each game:
The Bard's Tale: Tales of the Unknown
Combat was extremely dangerous at the very beginning and very end, but otherwise not very difficult at all. I didn't care much for the dungeon layouts, which seemed to be just random collections of floors and corridors, though I know they are not random dungeons. Still, a fun time overall and getting mass damage spells was akin to when you first get Fireball in Pool of Radiance in terms of sheer destructive ability.
The Bard's Tale II: The Destiny Knight
Much of the challenge of this game comes from mapping puzzles and the "solve or die" snare traps you need to beat in order to get the parts of the Destiny Wand. Your party ends up being overpowered for 90% of the game, whether you transfer a party or not, and I liked the dungeons even less than in BT1 as they just seemed to be constant spinners and dark/anti-magic/anti-song squares.
It was worth going through, though, because...
The Bard's Tale III: The Thief of Fate
Far and away my favorite of the series. By the time you're playing this game, you have a seriously impressive spellbook with lots of helpful tools to control battles, and you'll need them as even an imported party will face some challenging battles. The dungeon layouts are by far the best in the series, as many of them are quite memorable while still being large and enjoyable to explore. Finally, the game ends with some difficult but extremely satisfying encounters where you have to eek out every advantage you can just to get through.
The Bard's Tale IV: Barrows Deep
Let's start with the positives. Character building is quite a bit more interesting than in BT1-3, as even a single level up can mean a significant increase in power or ability. Combat also has the potential to be much more interesting, and it can be a lot of fun early on in the game carefully selecting abilities during combat to maximum your damage. However, you will typically earn every useful ability before you're even half way done with the game, so for the second half of the game you are not really making any interesting choices.
I also hate how Bards are handled here. In BT1-3 your Bard provides you with free buffs that last until you have him sing something else, even inside/outside combat. In BT4, a Bard is basically a fighter/wizard, and that strips away what made Bards really interesting in BT1-3.
The game has a lot of logic puzzles (i.e. sliding blocks and other puzzles of that ilk). I didn't mind them at all in the dungeons, which I felt had a good balance between combat encounters, smaller puzzles, and typically one large puzzle. The problem is that these puzzles are all over the outdoor areas, as well, and by the time you are 5-10 hours into the game, you've seen every single type of puzzle the game has to offer.
The Bard's Tale IV: Director's Cut
Really quite an improvement over BTIV that addresses every issue I had with the game.
The Director's Cut allows you to skip most if not all of the logic puzzles. I did all the logic puzzles during my run through BTIV, so I skipped all the mandatory puzzles and just did the optional ones this time around. The game honestly played a lot better without the puzzles.
I had a lot of performance issues with BTIV. BTIVDC fixes this, and I had a solid 30-60fps throughout the entire game, with most indoor areas a solid 60+fps.
My other major issue with BTIV was that loot and character development stalled about halfway through the game. BTIVDC seems to have rebalanced things, so that you always have something to look forward to. Unlike with BTIV, I continued to find loot that was a clear upgrade over what I was carrying throughout the entire game.
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All in all, I'd rank the games thusly:
BT3 > BT1 > BT4DC > BT2 > BT4
[EDIT] Added thoughts on BT4 Director's Cut