saying that Lopez wasn't a main factor in Opeth's sound would be bullshit. just listen from MAYH onward, you can hear his typical drumming, amazing stuff. and since Opeth has waited for so long giving Lopez time to make his choice, shows that they also feel this way, and wanted him to stay in the band.
thus it is a shame that he is gone, I'm looking forward to what he will do in his musical career in the future.
but these things happen and a new drummer, with a totally different style will give Opeth a fresh sound in some way I think. so I look forward to what the result will be. the guys in Opeth wouldn't have chosen Axe if he wasn't capable of doing an amazing job, so I have complete confidence in it. but I am really curious!!
the thing that bugs me the most though is that I have never had the chance to see Opeth live with Lopez .... it's a shame ....