Memories of Ice takes place at just about the same time as Deadhouse Gates did. However, instead of following along with the story of Fiddler, Kalam, Crokus, and the Whirlwhind Goddess in Raraku we instead travel amongst the mixed company of Caladan Brood's army intermingled with Dujek Onearms "outlawed" Malazan forces. It seems everyone in both books has figured out that Dujek's army was outlawed for expediency so that the two forces could team up to face off against the suicidal and fanatical forces of the Pannion Seer.
Considering the Brood army and the Dujek army have been busy fighting a war for the past decade or so it is understandable that there are some issues that need to be ironed out in the trust department between the two leaders. However, Wiskeyjack seems to forge a bridge between the two armies as Caladin (and his lieutenant, Anadomer Rake) find they truly like and trust Whiskeyjack.
While the first book focused on the city of Darujistan this story seems to have a fulcrum around the doomed city of Capustan which is guarded by the able, but undermanned, forces of the Gray Swords. The Gray Swords are an army of mercenaries sworn to the Fener, the God of War. Unbeknowst to them Fener is a fallen God while his rival Treach, the God of Summer, is rising. Fortunately for the Grey Swords they manage to find unexpected allies in the forces of Treach while defending Capustan.
The seer seems besieged on all sides as he faces down the Malazan's and their allies near Capustan a powerful and mysterious woman, Envy, has gathered about her a small band of impressive warriors that manage to cut a sizable swath through the Pannion's forces as they move toward the Seer's capital of Coral.
As the wars of mortals takes place the T'lan Imass, an undead legion of peoples sworn to destroy all Jaghut are called to the second gathering where they hope to be relieved of their eternal curse of non-life. The summoner for this gathering just happens to be traveling with Whiskeyjack's forces - a fortuituous pairing considering the deadly allies the Pannion is employing in his war against all who oppose him; the K'Chain Che'Maille.
If all of the odd ethnicities and nationalities are a little confusing - it's ok you aren't the only one. Erikson doesn't do a lot to really explain each group other than to give you a rapid introduction to them. Thankfully, if they are non-humanoid in appearance he at least gives you that much information.
Erikson also doesn't give you a lot of time to breath in stories. There is always something important happening or preparing to happen. You can skim over some of the descriptive fluff if that's your style but don't skim for more than a paragraph or two lest you miss the opening to a great confluence of peoples or events that set the stage for even greater moments.
So far in the three books we have met the forces of the Malazan Empire, the people of Pale (who fought the Malazan's), the people of Darujhistan (who also opposed the Malazan encroachment), Caladan Brood's armies, the Tiste Andii and Anadomer Rake, a couple Jaghut's, K'Chain Che'Maille, the army of the apocolypse in Raraku, a single Toblaki (some other race), the Pannion Domin's forces, the tribal Barghast, insect like Moranth, Gods, Ascendants, and quite a bit more. It can be a bit overwhelming at times but, at the same time, it all ends up making sense. So if you start to feel intimdated by the sheer scope of the novels stick with it - I don't think you'll regret it.