Strong suits of the books, in my opinion, include first and foremost Erikson's habit (although it can admittedly be maddening as well) of intentionally giving the reader only part of the picture at any given point, so that you always have to figure some things out for yourself, and when reading later books constantly come across things that make you reevaluate events in earlier books.

Other than that, he's terrific at writing "epic" scenes and characters, with tons of great battle scenes, duels, heroic stands and whatnot - in fact, he's made it an actual rule of the universe his books are set in, that there are periodic "convergences" of powerful characters, armies and (demi-)gods converging in one place and having a big showdown, which is always at the end of each novel. Some of his characters are really good, although there's such insane amounts of characters that inevitably some of them start to blend together, and there are (too) many who fail to find an individual voice. And thematically, he has many interesting scenes and thoughts about things like the rise and fall of civilizations (his universe's backstory goes back a million or so years, so there's room for rather a lot of fallen civilizations), the horrors of war, the comradeship between fellow soldiers (there seem to be some influences of American military journals of WW2, or at least that's what it feels like to me), and so on.

In what I and many others feel is the best book of the series, Memories of Ice (the third one), to take just one example, there's an amazing balance between intimate character moments, epic battles, surprise plot twists and thematic strength. I personally felt that balance was lacking too often in the later books, but even the weaker Malazan novels are still better than most fantasy books.

As for a satisfying conclusion, it's basically what one might expect based on what I wrote in the first paragraph: the conclusion of the main series is certainly suitably epic, and it makes you reevaluate most everything that came before. It doesn't tie off remotely every plot line, though, since both Erikson and his co-creator of the universe Ian Cameron Esslemont are writing other books/series set in the universe. Erikson's own new series is a prequel, but Esslemont's books that are out so far fill certain gaps in the main series and continue some plot lines where they were left off.