He drove a brilliant season this year, his best yet I think. He has made this Mercedes look alot better than it actually is.
Next year should be really good. Honda will (apparently) bring a serious BHP boost to Red Bull who very clearly have the best chassis, so they should challenge with Verstappen. Ferrari bring in Leclerc who will certainly be a much more serious challenge to Vettel than Kimi has been, nobody really knows how good he is because Ericcson is not a very good driver to judge him against.
If all three teams are relatively even, then we could be in for a four way title fight (Gasly and Bottas are not good enough to compete with their team mates imo).