Warmachine and Hordes have a lot in common, so I describe both in this post. We played the MkII version of both rule systems.
Both games are set in the same world, Warmachine describing the "civilized" and technologically (steam engines and fire arms mainly) more advanced factions, Hordes the more "primitive" factions.
Ruleswise, they are the same for almost anything. Single based models, small units or individuals, I-go-You-go turn sequence; rolling 2d6 and adding a stat vs. a target numbers covers most rolls.
What makes these rules special, they were the first wargames rules I played, where there was so much interaction between your models. There are some models that can just fight, but many models have effects on others, some can't even fight and only bestow buffs on others. You cannot play WarmaHordes without deeply thinking about these interactions and incorporting them into your strategic planning.
In Warmachine, you have your Warcaster (commander of your force, a magic user), and Warjacks (steampowered robots with limited intelligence). In Hordes you have your Warlock (commander of your force, a magic user), and Warbeasts (big monsters, which are tamed or in alliance with the Warlock). Then both types of forces have units of common soldiers, and some solo's, powerfull individuals.
The main difference is the interaction of Warcaster/Warjack and Warlock/Warbeast:
A Warcaster has a certain amount of Focus, he needs to allocate at the beginning of the turn among himself and his Warjacks. Focus allows the Warcaster to boost attacks, and to cast certain spells; Warjacks can boost their attacks, and can perform powerattacks, which they can't without focus. You never have enough Focus for what you want to do, so Warmachine is about managing a scarce ressource.
A Warlock has no such problems, where Warjacks have to spend Focus that was assigned to them, Warbeasts can do the same (boosting attacks, power attacks) just like that – but they accumulate Fury (same amount of Fury a Warjack would need to spend). But, and this is a big BUT, with too much Fury, the Warbeasts go berserk and out of control of their Warlock, they will even attack models of their own side. The equivalent of a Warcaster allocating Focus, is for a Warlock to leach Fury. At the beginning of a turn, where a Warcaster allocates Focus, a Warlock can leach Fury from Warbeast. After leaching, which is limited in the same way as the allocation limit of a Warcaster, Warbeasts with excess Fury an go wild. Not generating any Fury in a turn, leaves no Fury to leach by the Warlock, which means he cannot boost attacks, use spells etc. that require the expenditure of Fury. So Hordes is about managing your risk.
Both Warcasters and Warlocks have a Feat, a unique and very powerful ability they can use once a game. These Feats can have a big impact on a game – if played at the right moment.
You can play games with Warmachine vs. Warmachine forces, Hordes vs. Hordes forces, and games with Warmachine vs. Hordes forces.
With the great interaction of models described above, and the Feat of your commander, taking the same force, and just exchanging one model, might completely alter your strategy and game flow. This game has a lot of replayability.
As you can see from the AARs, we played this game quite a lot for some time, before due to time constraints the interest petered out at some point. But I keep these times in good memory. Especially at the beginning, where the game was new to all of us, we played with the starter force we painted up, and also agreed to play a couple games with the same models, to get into the game.
But when it started, that each player brought one or two new models for a game, everything changed up. The controller of the new models needed to learn how to play them, the opponent needed to learn how to counter them. Sometimes, one player would bring a new model, to counter a new model from the previous game the opponent brought – especially helpful, when this specific model wasn't in the current game. These were good times…