Hmm, while I do think Bannerlord has quite a few very unnerving bugs like crashes (although I had only one in two days), corrupted saves and the steamroll, I have played a few Early Access games and can say that it is in a comparably good state right now.
The base sandbox is complete and working. Once they patched the steamrolling and the corrupted saves, everyone can spend 100 hours into one campaign and experience every aspect. This is likely the next patch and rolling out in the next couple of days.
Other than that the only things missing right now is what I call "fluff", the stuffing around the edges. There are many quests missing, the leveling system needs balance tweaking, the general game world and mechanics (hideouts) need adjustments and some mechanics appear to miss or are not deep enough (clan tab). Also the optimisation is poor right now with too many and too long loading times, I do not know if this will improve significantly.
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Now the most obvious comparison is with DayZ, that was released as basically just a sandbox and many more placeholders, which turned the game into a 3rd person hardcore shooter, I mean they had to remove zombies, the staple of the game, for multiple months.
SCUM is a similar game in that genre, and while more feature-complete than DayZ has a lot to do and is also months and months away from full-release.
Ark released in a similar state as Bannerlord, yet I dare say Bannerlord is more feature complete, and Ark did only receive patches every month or so, while some core mechanics are rather broken (path-finding, collision and the resulting over-importance of flyers), with no real ability to be fixed.
Subnautica launched with a bare minimum of area to explore and features implemented, however, the core experience was so new and beautiful, that people hardly realized and checked in every month to be continually amazed.
Minecraft release just as a barebones sandbox, with basically no features, yet the base sandbox is entirely what is the core and what keeps people playing and had constant fluff updates that only add to the basegame.
Rimworld, probably the most comparable of the bunch, started also with core sandbox that was working, was very attractive to play and constant patches added content that would make you not only see whats new, but also play what's new.
Bannerlord sits, in my opinion, in a similar niche, the base sandbox is the core and works fine at the moment, every patch will just continually add to it (and fast too, it appears) and when the two major things are sorted out you can enjoy that indefinitely and every patch will just generate more content.