It's the first one in a long time that people seem to like, box office isn't bad either.
Rotten Tomatoes has not been a credible source for what people like since, at the latest, their running cover for Captain Marvel. Remember how they removed the "Want to see" part of the site after it dropped to 28%, claiming it was being treated as the Audience Score which was clearly a lie - it was explicitly labelled "WANT TO SEE", i.e. clearly stated that the film had not been seen. RT also denied this change had anything to do with Captain Marvel and then, a fortnight later, stated in an unrelated context that the change had been "brought forward" due to the Captain Marvel situation.
The Critics part on the other hand is actually misleading in that the 88% doesn't mean that critics as a group think it's a 88% (i.e. 88 out of 100) film; it means that 88% have given it a fresh rating (better than 5/10, 2 of 4, or whatever metric they use. That's why it's often a fun game to look at what "fresh" critic reviews actually say and marvel (no pun intended) at how reviews that are wall to wall criticism or only praise the politics of a film are counted as fresh.
Add in some very curious site behaviour such as the locking of declining audience scores and the delaying of scores appearing and it's clear that RT is not a neutral data presentation site. It's a PR/marketing operation for the industry Disney seeming to get particularly preferential treatment.
Box office not bad? By what metric? As matters stand it's more of a flop than I am when I see Zendeya on screen. In non-adjusted terms it's scrubbing along with (actually towards the bottom end of) the "they lost money" dregs of phases 4 and 5. In real terms (inflation adjusted) of all the MCU films from the very start of phase 1, only The Marvels has had a worse first weekend.
The "good" word of mouth seems to revolve around one, well it's not as bad as other phase 4 and 5 stuff; two, it deals with depression; three, Florence Pugh is great; four, the MCU is back to form. The first is damning with faint praise; being punched in the face once is not as bad as being punched in the face twice - it's still not good. The second is a so what comment regardless of whether the approach to depression is handled well or in the most superficial and Californian of ways. The third, well great but if anyone thinks any appreciable number of people are going to buy tickets because Florence Pugh is in a MCU film they're deluded. The fourth, well that's just the mantra that's trotted out with every recent MCU film, gets proven wrong and quietly forgotten about a couple of weeks later.
It might be that Thunderbolts* (sorry, The New Avengers now) will have a spectacular run and I'm interested to see what, if any effect the name change which might be seen as a tad desperate, will have on the second and subsequent weeks. As matters currently stand it needs a run the like of which the MCU has not seen for many years not to be another loss maker.