Early Access is a service within Valve's Steam platform where developers can publish their games before they are finished for the purpose of getting feedback before the full release. While this may seem like a solid idea on paper, in practice it has become a horribly exploited system that makes it easier for cash grabbers to make a quick buck on Steam.
The idea behind Early Access is that a developer can make a game currently in development available for the public so they can get a feel of the game's mechanics and feelings and in turn give the developers some feedback for improvements that can be done before the full release. However, the developer ideally should release the game when it's in an advanced beta near full completion, then use the feedback obtained to finish the game. This is almost never the case, however, because some games in "Early Access" state can still cost money or have microtransactions.
Most of the time, some games in "Early Access" are thrown out rushed and blatantly unfinished. Cash-grabbers can easily make quick shovelware full of bugs and glitches with barely any work, call them "Early Access" to make some quick sales under the promise of "the game will be completed later", then never actually finish the game. Most of the time some games in Early Access are never fully released because some developers already made money off of it and then they decide to just go make another game rather than finishing the current unfinished one. In later years, the practice has become a cheap excuse for developers to rush out unfinished games then start making money off them as quickly as possible without any real intention of ever making a real finished product.
A bigger problem that has risen due to Early Access is that now some people have become more forgiving towards rushed unfinished games. There are many people that mistakenly believe that when a game is in "Early Access" that means it should get a free pass from technical issues, bugs, glitches, rushed mechanics, etcetera even when some developers are obviously using Early Access as an excuse to sell unfinished products or put microtransactions on rushed cash grabs. Others claim that a game in Early Access shouldn't be reviewed because "it'll be fixed later"- While it is true that a game in Early Access should be expected to have a few issues due to not being a finished product, that doesn't mean that some developers can release blatantly unfinished garbage and not be criticized for it.
Obviously unfinished games that were released long before they were ready have become more common even outside Early Access, and unfortunately many have attempted to excuse this by claiming that those games "are Early Access" even though they were full price products published and sold on stores. Even some games blatantly admit they're unfinished in the retail release yet still attempt to use the "Early Access" excuse to get away with it.
However, despite Early Access getting a bad reputation, there are great games that can do this trend the right way. Killing Floor 2, Rust, DiRT Rally, BeamNG.Drive, Factorio, Besiege, Black Mesa (the Half-Life remake), The Long Dark, Starbound, Subnautica, Deep Rock Galactic, Space Engineers, Wreckfest (previously titled Next Car Game), TABS: Totally Accurate Battle Simulator, POSTAL 4: No Regerts, Them's Fighting Herds, Hot Dogs Horseshoes & Hand Grenades, Squad, Kerbal Space Program, and some others are all great games that are in Early Access but are actually great, and their developers don't leave them unfinished and are perfect examples of this trend.