Very buggy releases, horrific writing, atrocious level scaling, and poor RPG systems, and yet not only do gaming critics fawn over them, their last three releases won the most GOTY awards for the years they were released.
Daggerfall was a buggy nightmare and a complete mess of a game, Morrowind was good despite many irritating flaws but no gem, Oblivion learns nothing of Morrowind's problems and has a broken leveling system, fallout 3 is the worst main fallout game in the series and completely inferior to Obsidans follow up, and Skyrim is an overrated mess fawned by critics while they ignore the many flaws.
When Bethesda games have bugs, they are conveniently ignored, no matter how game breaking they are, while Obsidian or some European RPG developers get crucified by reviewers for their bugs. Nevermind that Bethesda themselves made Obsidian rush New Vegas out. And really, why buy Bethesda games on consoles, where you can get screwed without the ~ commands.
Nevermind their atrocious writing and their noticeable decline in the writing department. Moronic quests, moronic plots, underdeveloped and stupid characters, need I go on. Sure a broken clock is right twice a day, Dawnguard is well written (Serana is great), but wow, most of their writing is bad. Fallout 3 is basically fan fiction in the fallout universe. Bethesda lacks the intrigue and maturity that CD Projeckt Red brings, lacks the poignant human element writing and elite character writing that Bioware has, and lacks the role playing smart writing or legitimate humorous writing of Obsidian.
And as RPGs, Bethesda games suck, The leveling system is broken, where skill systems are unbalanced, and leveling in Elder Scrolls games is tedious. And why level, it doesn't matter, because almost everything scales. this makes leveling absolutely pointless, makes the world less dangerous and intriguing, and makes quest rewards and loot pointless. And there are no real consequences for your actions (outside of Fallout 3 town wipes and somewhat Broken Steel), either through story decisions or exploring due to level scaling.
So all hail New Vegas, the best "Bethesda game" ever made.