The role-playing and writing are usually brilliant in Obsidian games, and you could say they blend the expansiveness of Bethesda games with the depth of BioWare games. FNV is the greatest Western RPG in my humble opinion. Perhaps Obsidian games give you the most freedom to shape the path of your character in the main quest. Obsidian games are also quite varied, they adapt to the style of the series they are covering. KotOR 2 has many of the strengths of a BioWare game (small choices matter/telltale style of gaming) and FNV has many of the strengths of a Bethesda game (large-scale open world with many engaging side quests). Obsidian games tend to have a solid faction standing system AND a morality system, and these add to game immersion and role-playing capabilities. When Obsidian try to develop original titles like The Outer Worlds, their ability to actually create and fully design a world is questionable. While that game is enjoyable to play through and had solid role-playing, almost everything about that franchise is forgettable. The characters are forgettable, the locations are forgettable, the factions are forgettable. The lore is uninteresting and shallow. Compare it with the worldbuilding of a similar game like Mass Effect and it's not even close.
Bethesda games have worlds that are the most expansive but also the most shallow. They tend to have great side quests, but their main quests aren't always very engaging or exciting and they tend to force you down the generic hero path. What I mean by shallow is player actions don't tend to impact on the world or narrative like they do in BioWare or Obsidian titles, which can be frustrating. But Bethesda games are arguably the most replayable if only because of the amount of content they have (locations, side quests, faction quests) and because their class system is good enough that you want to try out different builds. You can have a decent playthrough of Bethesda games while avoiding the main quest altogether, which is something you can't really do in BioWare games. Bethesda games tend to have many memorable characters and locations, and their game worlds are fully imagined with history and lore. Their games encourage you to explore the world you are in.
BioWare games have worlds where your actions have a strong and lasting impact. But I would say the narrative freedom they offer is more strategic than role-playing. For instance, in Mass Effect they challenge you to make smart choices but do not give you much creative freedom over the character you are playing. Their worlds are also probably the least open of the three developers in question. These two factors limit the replayability of BioWare games IMHO. BioWare games usually include a morality system which adds to role-playing capabilities.
To sum it up, in Bethesda games your actions don't have consequences. The main story isn't that important, your role-playing comes in the side quests you choose to play. The worlds are lovingly crafted but you don't have much impact on them. BioWare games are the opposite. Their games are very cinematic and the main story is everything. Every small choice, every dialogue option has an impact on the world, which is also lovingly crafted. Obsidian walk the line between the two. They are great at making games in already existing franchises/universes, but suck at creating their own.
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