Absolutely critical. A solid drum/bass core is a band. One of my favorite soapbox topics...
As a bass player, the first question I ask any potential band (long term or sub call, doesn't matter) who the drummer is. It's sort of a plus if I know the player to be a good, dependable person, and sort of exciting if I know the player has great chops...but meter is absolutely, irrevocably king. I will take a four-on-the-floor pocket drummer with flawless meter over a flash drummer with wavering (or drooping) meter all the time, every time, until the end of days.
I have experienced the latter type, as many of us have. It sucks the enjoyment out of music and the soul out of my being to be the train engine that's trying to drag the convoy uphill for an entire gig. And if I'm wise to a saggy drummer when the call comes, the answer is "sorry, can't do it." Without fail.
It probably sounds over-the-top nasty, but I feel that solid drumming really is that pivotal. My regular band includes a drummer who brings a cocktail kit to bigger gigs, and only a snare drum to smaller ones. His meter is exquisite. It doesn't matter a lick if he's doing a ballad with brushes or a shuffle with heavy sticks, the combination of his drumming + our vocalist's percussion toys + my bass has been described in a variety of positive ways. Most recently, I was approached by another musician who said it reminded him of a machine - just an unstoppable, bulletproof wall of groove, regardless of style. And that was with just snare, bass, and either tambourine or Eggz. You can get a lot out of a little when everybody falls into the same pocket and stay there.
I know a drummer is good if I can drop in some mildly syncopated riffs - or build a little tension into a line by playing 3 against 4 for a measure, or just any departure from the regular flow of the line - and the same groove is waiting for me when I return. That's the drummer I want to play with.
I once had the pleasure of catching Steve Smith (ex-Journey) with a jazz combo at a bar in Greeley, Colorado. He was getting very exploratory and taking some long, wild excursions, but what blew me away was his ability to land dead-nuts back where he started, no matter how long he'd been away. It was amazing to watch him work!
Solid drummer = great gig. Anything else = not so much.
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