I have played a few of them, and have actually beaten the main story on most of the ones I have played. Here are some thoughts:
Wizardry Gaiden 3 (GB): Imagine classic Wizardry, but with many (not all) of the races and classes from modern Wizardry. Of course, with the new races and classes, they introduced some of the same balance issues seen in Wizardry 6; Valkyries are really good (they level up faster than Clerics), while Rangers are terrible. Also, there's an overworld to explore which connects the dungeons. There are a couple things I should warn you about: First, you need to take a thief with you; otherwise, you will run into a door that you can't unlock, as ninja, ranger, and bard are horrible at unlocking doors, and unlocking doors is actually *required*. (A Faerie Bard can be as good with traps as a thief, but will be unable to deal with locked doors, and dealing with locked doors is mandatory.) Also, there's one puzzle whose solution feels like an exploit. Also, CORTU (and the similar alchemy spell) is broken and will make your spells less effective instead of making enemy spells less effective.
Wizardry Gaiden 4 (SFC): Adds more Wizardry 6 features, including the missing races and classes (you now have all 4 types of magic). At the start, you have access to 3 huge dungeons, which can be played through in any order. These dungeons each have (adventure-game style) puzzles to solve along with NPCs to interact with; sometimes there are multiple solutions to puzzles (thief-types can unlock doors that otherwise require solving puzzles, and you can attack and kill most NPCs). The downside is that the enemy strongth stops increasing once you've reached the most danagerous floors of a dungeon until you've cleared all three, making combat too easy and no rewarding enough for a while. Once you beat the first three dungeons, however, the NPC interaction element disappears; however, Wizardry 1 fans will enjoy what happens next.. Because of the NPC interaction, this game requires more knowledge of Japanese than the other games I'm mentioning here to fully enjoy; it's basically a Japanese-developed WRPG at this point. Also, *never* use the spell that removes curses; it has been known to corrupt saves.
Wizardry DIMGUIL (PSX): Basically Wizardry Gaiden 5. No more complex NPC interaction, and 1/4 of the spells have been removed, but the game feels much more balanced and doesn't have a long segment of combat being too easy. I note that this game is linear, though apparently beating a certain rather strong enemy will let you beat the game early (but do note that it will be obvious that you aren't ready to fight that boss when you can first encounter it). Oddly, there is a game-wide puzzle where there's a foreign script to decipher, but the messages in that script are in English, not Japanese. (In particular, that puzzle can be solved without Japanese knowledge.) The postgame bonus boss is said to be one of the hardest CRPG bosses that exist, and apparently the requirements to access the bonus dungeon are rather obscure. This is one that I haven't finished.
Wizardry Empire 2 (GBC): This game changes the mechanics a bit; spells (particularly healing) are more powerful, and HP gains after class change aren't as low. This game otherwise plays like the old games, except that there are some extra classes that require special items to change into; each has a unique list of spells that can't be transferred to other classes. Unfortunately, getting access to all those spells requires a rather high level. There are a few bugs, though not as much as in the first GBC Wizardry Empire. Note that the GBC Wizardry Empire games are *not* the same as the one on consoles.
Wizardry Summoner (GBA): This game had an interesting idea, being able to summon monsters as persistent party members that don't disappear after battle. Unfortunately, they made one major mistake when making this game which is enough to ruin it; they switched XP and GP rewards from enemies. As a result, it takes way too long to level up, far longer than any other Wizardry I have played, while you get tons of money and nothing to do with it. There apparently was an enhanced PlayStation 2 port of the game with different music (for whatever reason), which increased enemy XP awards a bit, but which appears to still suffer from the issue that it takes way too long to level up. Haven't finished this one because of this major flaw. (Maybe someday I should try hacking the game to swap XP and GP rewards from enemies, and see if that makes the game playable.)
