The rules are simple, the combat is streamlined, but it definitely has depth. Plays pretty quickly, as well.
There are two types of units; heros and squads. Squads are like groups of 4e's minions; several pieces which share the same stats but each die if hit. Heroes are single units which can take a certain number of hits.
Every unit has a point cost. The way I usually play is we set up all the units, then take turns drafting pieces with some point total in mind (e.g. 500 points).
A turn goes something like this (going from memory, so may get something wrong).
Roll for initiative-- straight d20 roll, some units give bonuses. Only time you roll the d20.
In initiative order, players take turn placing their four order markers. The markers are labeled 1, 2, 3 and X. The X is a decoy. You may put multiple markers on a single unit's card, if you like.
After all markers have been placed, the initiative winner reveals his first marker and moves and attacks with that unit. Then the other player does the same. Same process for markers 2 and 3, and then you roll initiative for next round.
Line of sight is done via looking behind the unit's head and seeing if he can actually see his target. Each unit's card has sillouhettes which show both where the line of sight is measured from, and what portions of the unit are valid for confirming line of sight (e.g. an archer's bow might not count, so if that's all you can see you can't hit it).
After taking into account all abilities and statistics, the attacker rolls so many red dice and the defender rolls so many blue dice. All dice are six-sided; the red dice have 3 skulls and 3 blanks. The defender dice have 2 shields and 4 blanks.
Each shield cancels one skull. Any leftover skulls are applied as damage. In the "minion" units, a single skull will kill a piece, in the hero units you put damage markers on their cards.