The game takes place in Ireland (hence the title). The various tribes are warring amongst each other, but over everything lies the shadow of Balor of the Evil Eye. Every year he forcibly takes tribute, and his Fomorians are free to raid any of the provinces. Your goal is to unite all of Eire and defeat Balor.
At the beginning of the game you get to pick a tribe to be the leader of. The different tribes start with different numbers of heroes and different numbers of provinces. Eire is divided into a lot of provinces - at least 50, possibly something like 64. Each tribe has several heroes, who are named after various figures in Irish mythology. There are 3 kinds of heroes: fighters, druids, and bards; fighters can't spell-cast but, during battles, can engage other fighters in duels. The heroes have levels, stats, and small armies (squads?) associated with them, and they can be equipped with items (sort of like relics). There are also wandering heroes who move from province to province. Wandering fighters can be dueled with to train your own fighters (for a fee of several cattle), and druids and bards can be paid (in cattle) to reveal information about spells or legends. All of them can be asked for news (e.g. "Which tribe seems to be most powerful right now"). I have *no* clue what wandering heroes do with 35 cattle.
There are two modes during the game - province and battle. Obviously most things happen in province mode. Heroes are really important. In province mode, they can be ordered to farm to get more grain, herd cattle to increase the amount of cattle, train for fighting, chop wood, mine metal, scout adjacent territories, cast province-mode spells, build up the burg (main village) or citadel (main administrative building), or rest. Everything except resting and casting takes up hero Strength; casting takes up Mana (obviously); rest regenerates both Mana and Strength. Heroes can also be made to create items; the kinds of items they can make depends on their class, level, whether they have Craftmanship or something similar, and intelligence (or maybe it's Dexterity). The different activities will help develop different stats (e.g. training builds up Might). Heroes can also be sent to other provinces to pay tribute to (good way of building up Diplomacy), for trade (also a good way of building up Diplomacy, and you get stuff for it too), to raid cattle, or to wage war. They can also settle empty provinces.
Battle mode is, well, battle mode. To battle, you pick up to 7 of your heroes and some amount of grain (if you run out of grain or 7 days pass without a clear winner, you go home), and send them to a province. One of the heroes you pick to be the combat leader; if s/he is captured, you lose the battle. In each battle turn, heroes can move and take an action; if they take the action first, they can't move afterwards. Actions include spell-casting, simple melee combat, dueling, defense (try to rest to recover strength and mana, but will fight back when necessary), rest (what it sounds like, you're very vulnerable when you do this), encouraging comrades (helps to recover strength), taunting, switching equipped items with another hero, and retreating from the battlefield. You can win by capturing/defeating the enemy leader or, if you're defending, if you manage to hold out for 7 days. (2 turns per day, there's a night-time where heroes recover, helped if they have good druids.) For a quick victory, just go for the leader; if you want to recruit heroes, try to capture everybody. At the end of battle, you talk to each of the heroes. You can ask them to join you (they may refuse depending on relative hero levels or tribe rankings), release them, or exile them. Tribe leaders can be recruited only if their last province has been defeated and there are no empty provinces on the map, and even then they may refuse to join. (In that case, they'll start showing up as wandering heroes.)
Spellcasting uses runes. There's a 4x4? array of runes - 4 types of runes and 4 of each type. Then you pick an element - druids get Earth and Water, bards get Air and Fire. You pick one rune of each type, and then an element, to cast a spell; only specific combinations actually do anything. Different combinations might do different things depending on if it's battle or province mode. Spells can be really useful, both in and out of battle... Bards can increase the amount of cattle or population, druids can re-grow trees, redirect water, or heal, and of course both have complements of damaging spells.
I like this game a lot. I've actually beaten it, although I suppose I sort of cheated. The first time I played it with my brother; I chose Manannan of the Fionnaidh as my tribe leader, and my brother chose Finn of the Fianna. This is a pretty good combo to play cooperatively, since the two tribes start with a large number of heroes (although not many provinces) and are very close to each other in the map. Eventually my brother got tired, so I wound up taking over for him, and merging the two tribes. (One of the possible things you can do is ask another tribe to join you; for a while they'll retain control but take suggestions from you, but eventually they'll let you control them directly.) I think it's cool that you can get through a lot of the game on diplomacy, exchanging tributes and trading to build up high peace levels with other tribes, and then merging them. Unfortunately, you can't quite win the game like that - you can theoretically unite Eire with just diplomacy, but then you still have to battle Balor and his cronies. I've lost a lot of sleep thanks to this game, but now it won't run on my new system (WinXP? + old DOS game = game not happy).
I think I like CelticTales so much because of its focus on Heroes. I'm an RPG nut, so including characters that can be improved is appealing to me. It's probably sad, or maybe scary, that (at least for a while, maybe not anymore), I could name by face portrait all of the heroes in the game, as well as their character class. :P I guess HeroesOfMightAndMagic? also concentrates on heroes, but it's all combat-based. I like the province-building aspect, although I haven't quite figured out the point of increasing your population... It just kind of happens...
It's rather funny that Dierdre (there was a legend about her... She was a really really beautiful woman and then some guy whose name I can't remember fell in love with her and tried to steal her away) is a Fighter, and really good one, too. (She starts out at a MUCH higher level than any other hero.) Some of the other assignments are also kind of weird, like making the Morrigan a fighter. I think they usually did pretty well with the bards and druids. Some of the hero/tribe assignments work really well. The Fianna are probably the best case (or at least the one I know the most about) - Finn, of course, and one of his lieutenants, Goll MacMorna?, his son Oisin, another of his men, Diarmuid, who was his rival for some girl whose name I can't remember right now...
Anyway. I like this game. I wish I could find it again and find a system that will run it.