First, its very rare for a game to be overwhelmingly positive in steam reviews, and even harder for an MMO to get that.
Everyone knows the real success isn't in the number of people playing, but how many people are reviewing in a positive way. Sure, there is a good percentage that don't like BDO on Steam for various reasons. That is true for any MMO. MMOs especially are either hate or love them, so they'll never be overwhelmingly positive even if to someone its the best MMO in the world to them.
However, this is a very good sign for BDO that the reviews are mostly positive
Compared to EVE where its mostly positive, but recent reviews its "mixed". Same with Ryzom (which is a freemium MMO and free on Steam), which Ryzom was very badly reviewed when launched on Steam and is in even worse shape than before the Steam release. Of course both of these have been out a lot longer on Steam than BDO has been.
What is a fact however, is as of now, like EVE used to be (but no longer), new Steam launch and reviews are mostly positive feedback. Maybe it will change as people play the game, maybe an update will come out and it will receive major backlash, that could happen to any MMO. And it isn't because its just a new MMO on steam, plenty of new MMOs got on steam and were reviewed very poorly (like Ryzom, which didn't even cost money).
This is a very good sign for BDO, of course maybe like EVE, people will hate it as time goes on. But as of now, the large majority of reviews are positive and most people are really enjoying the game and the Steam release. Even if numbers go down, if reviews remain good, that is where the true test comes in.
My Skyrim, Fallout 4, Starbound and WoW + other game mods at MODDB: