The Warriors are a strange, underrated team. They were the best team in basketball by defensive rating, and 17th in offensive rating, which is probably surprising to some people. The defense has probably gotten better during the playoffs, thanks to the resurgence of Looney. They do have some weaknesses on that end, especially at the guard positions; with Poole being a guy that Kerr has to be careful with because they kind of need his scoring, but he's a liability on defense and can be exploited in mismatches.
Curry has been very good (both in the regular season and the playoffs) but not his typical supernova self. The Warriors team is balanced; guys like Klay, Poole and Wiggins contribute 15-25 points a game each; and help carry GS to victory. That will be unlike the last few rounds for the Celtics, who have been met by incredible individual play by Butler/Giannis, but been salvaged by nobody else being capable of scoring. The other major difference is that the other teams were very physical on offense, with big wings crushing it in the paint, while the Warriors are more of a finesse scoring team.
The worry for the Celtics is of course health, and guys just wearing down. They need Brown/Tatum to abuse the few weaknesses in Golden State's defense, and then rely on their steady, inflexible team defense to stifle Golden State. The hope for the Celtics is that their physicality and battle-tested rigor will surprise Golden State early in the series and lead to them gaining some footing and stealing home court. Of course, GS's core is still as experienced as it comes in the Finals, so I doubt they will be that shell-shocked.