These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
First Installment Wins: Galactrix, Puzzle Quest 2, and Kingdoms aren't even in the same league as Challenge Of The Warlords.
Game Breaker: Equipping a Rune of Music item and a Rune of Jewels item gives you attack capabilities on par with a Runekeeper's.
That's nothing. Try forging something with the Rune of Music and the Rune of Dragons. You'll be getting six mana of every color when you match four or five gems. Combine this with Deathbringer, a high red mana maximum, and items that give you extra red mana at the start of each battle, and you can kill just about anything that lacks spell resistance (and many enemies that have it) in a matter of seconds. In fact, it's possible to match so many skulls in a row in so many different directions, the PSP version will crash just trying to keep track of the numbers.
Along the same lines, Rune of Orbs + Rune of Dragons = you get 6 mana of every color every time your opponent casts a spell. This gives you a lot of leeway in responding to your foe's actions.
Forging shmorging, try Berserk Rage > Deathbringer sometime; on non-resistant and/or unlucky foes, it can easily tear them apart, given enough red and skull pieces already on the board (and as the warrior, your battle skill will make the 4/5 chains of skulls even more impressive. Likewise, monster spells can also be highly potent; Conflagration allows you to turn any type of board item (gems, gold, experience, and skulls) into red gems, Headbutt will destroy all red gems and cause your foe to lose one turn plus one for every eight red gems on the board destroyed, and Charm/Eat Skulls can restore your life or increase Battle skill respectively at the cost of destroying all the skulls on the board (+1 Life/Battle per skull). Not that there's really anything wrong with items, though.
Bards. Bards, bards, BARDS. Every bard starts with Inspire, a spell that is extremely cheap and has the seemingly balanced effect of increasing all your skills by an amount determined by Yellow Mana at a 1-10 ratio. The problem arises when it turns out that this rise lasts the whole battle, and it stacks, and that the skill increase MAKES IT EASIER AND EASIER to get more skills, resulting in a situation where the bard becomes something of a small god, gaining absurd mana for matches of three, dealing insane damage with simple skulls, and getting extra turns and wildcards everywhere. Oh, and it affects Cunning, too, meaning that once you win with a bajillion ranks in it, you get 300x the money and experience you would have. Then again, you kind of need it, since, you know, The Computer Is a Cheating Bastard.
Or simply ride a Giant Spider and crack out Web > Berserk Rage > Deathbringer, with a high enough Yellow Mana to give yourself plenty of spare moves. Armed as such from Level 30 (when this configuration becomes available), most fights become laughably easy.
It's worth noting that the previous examples mostly refer to the Warrior only (that's the only class with access to Deathbringer).
Plague Lord brings the pain with the Thief's Cowl — doubles damage done while Hidden. The Rogue class has Hide as a class spell. You can also get Hide from a Scorpion mount or learned from a goblin. Keep in mind that being hidden already doubles your damage, so the Cowl brings the damage status to quadruple. It can make a standard skull attack hit for 18-20 points, without enhancing weapons. Add to that any of the above uber-spells or weapons and you can pretty much wipe out an enemy with one turn.
And then there's the Rogue's Bribery spell, which turns all gold to skulls (and all stars to water gems). This plus the above Thief's Cowl/Hide scheme plus waiting to use it until you'll get a 4-of-a-kind in the process = pain. Add in the Frostblade (amplifies damage based on how many water gems are on the board) and... well... Follow up with Frostbite (learned from Frost Giants, destroys all water gems for an equivalent amount of damage to the victim) to add insult to injury.
The Pegasus mount's Ascend spell (turns red and green mana into purple stars) matches nicely with Bribery (With a decent cascade, it somehow always leaves a good amount of coins on the board).
Or you can swap the Frostblade for the Stiletto, which does -2 mana for every 3 damage you do. A decent strike with the Hide/Cowl/Bribery combo can knock any opponent's mana gauge down to zero. VERY handy when facing Runekeepers, Citadels, and uber-spell-happy bosses.
It should be mentioned that the above mention of Bribery also works with any spell that turns all of a specific gem type into skulls, such as the wizard's Flaming Skulls; the Berserk Rage that the Warrior can learn naturally, and anyone else can snap up through a Minotaur King; and the learned-from-a-Medusa Stone Gaze. As long as you have Hide by equipping a Chameleon Ring (you have to make a 4- or 5-of-a-kind first, though), or courtesy of a Goblin or Giant Scorpion, these spells will do just fine.
Roll the class that learns Deathbringer. Stack yourself with equipment that starts your red mana pool high and regens red mana when you combo. Enjoy the fireworks.
In the Mobile Phone version, the Knight class gets "En Garde", which has low cost, turns four random gems to skulls, and does not end your turn. So, if you have a decent amount of mana, you can cast it repeatedly to turn upwards of 30 gems into skulls without ending your turn, setting yourself up for ridiculous skull-combos.
Speaking of the Knight, Paladin's Aura. Gaining 2 mana of every color per turn is far more useful than it sounds. The only problem is the steep startup cost (9 blue mana and 12 yellow mana), but after that, it literally pays for itself.
Hand of Power + Fireball = 3 or 5 damage per blown-up skull, depending on whether you cast Hand of Power once or twice. This is far superior to matching skulls normally, and handily makes up for the Wizard's piss-poor Battle skill. Once you have high enough Air and Fire mastery to cast repeated Fireballs after a couple Hands of Power, you can seriously wreck an opponent. The only problem is that Hand of Power lasts a mere 10 turns.
PQ2's Wyvern and Manticore poisons. Maxed out and wielding different types, they can inflict up to 28 unblockable points of damage per turn.
The Assassin's five Strike spells. Under the right board conditions, you can cast strike spells (one for each color mana, hitting for 1-4 damage per gem) until you run out of mana, basically the puzzle game equivalent to Stun Locking.
Goddamned Bats: In Puzzle Quest 2, ghosts like to spam a spell that turns nearly a quarter of gems on the board blue, giving them an excellent chance of receiving another turn. It's not uncommon for you to sit and watch while they take several turns in a row.
Even worse? The Yeti has this same spell. And it's healed by matching blue gems. Thank God it's a Bonus Boss.
Good Bad Bugs: In Puzzle Kingdoms, the game will occasionally automatically add spells, artifacts, or relics to your Hero, as long as there's an empty slot for it, allowing you to go over the points cap for that kingdom. This only lasts until the next kingdom, though.
It's Easy, so It Sucks: Puzzle Quest 2. Even on hard, this game is A LOT easier than PQ or Galactrixnote Unless you're playing as a Templar, which still isn't that hard, outside of the Bonus Bosses, and the AI is a lot worse.
Nightmare Fuel: The screams of attacked and killed enemies in Puzzle Kingdoms.
Periphery Demographic: A really weird attempt is done for Puzzle Quest 2. This game is meant to appeal to hardcore PVP players and people who found the first game too demanding at the same time.
Porting Disaster: The PSP version of Challenge Of The Warlords is just as good as the other versions, except for one bug: The partner "support ability" system doesn't work.
The Wii version somehow managed to have smaller text than the DS version on many TVs.
Scrappy Mechanic: In Galactrix, not a single review will fail to mention the annoyance of having to gate repeatedly. And to make it better, they sometimes make you gate up to 6 times in a row! Oh, and there's no reward for it, either.
Sequelitis: Just as there was a gap in quality between Challenge of the Warlords and Galactrix, there's a gap between Galactrix and Puzzle Kingdoms. Though at least there's no minigame to pad things up.