For anyone who might think the drummer is generally a disposable/replaceable part of a band, witness Slayer. Original drummer Dave Lombardo has rejoined them on their new record, Christ Illusion, for the first time since 1990's Seasons In The Abyss and the difference is striking. Not to impugn the skills of Paul Bostaph, who took Lombardo's place, but something always felt… missing. Christ Illusion just feels like a Slayer album for the first time in, well… 16 years. It's as brutal and unforgiving as anything they've done, which, if you can say nothing else about Slayer, it's that they've never compromised and never tempered their style to fit any trends.
Frankly, I feel Dave is the only thing that even held the band together in their early years. While Jeff Hanneman and Kerry King have grown into probably the tightest guitar team in metal today, perhaps ever, they were a bit… young when the band first started. It felt sometimes like their reach was just slightly exceeding their grasp, and it was only Lombardo's impeccable skills that pulled things back and held them together. With a lesser drummer I suspect the band may have derailed and fell apart. Again, I don't mean to impugn anyone's skills here, I have nothing but respect and admiration for both guitarists.
So, yeah, drummers matter. Slayer without Dave Lombardo are an amazing band, but with him they are legendary.