In the name of the Pizza Lord. Charge!
What to do now, buy it again on Kindle to read it again or go straight to Deadhouse Gates?
I recommend Malazan wikia. It has this superbly detailed summary by individual chapters and they even made sure to include the poems or excerpts that start off every chapter.
If you read the summary, you will probably recollect more of the book than you do now and even if you don't recollect as much, this summary is so detailed you can comfortably go to Deadhouse Gates without being lost as to who is who.
Deadhouse Gates has only a few characters from GotM. The majority is new characters, and the novel is set in a completely new continent, so it's a fresh start on many levels.