I have only recently 'discovered' the litrpg genre (for those unfamiliar with this, the most similar examples I can give are Overlord, SAO, and Log Horizon) of novels.  As such, I'm not going to presume to review things like stat systems and how the stories 'played'.  It would be ridiculous for me to do so (since I'm not a min-max freak who loves all that math), and it would also be boring as hell to listen to here, lol.  I will note some classic tropes:  Protagonists who jump to wrong conclusions about the 'systems', meaninglessly horrific tribulations that seem tailor-made to force the protagonist to grow, a higher tendency toward gamer brain (dual-thinking amorality, a tendency to consider people not from Earth to be soulless NPCs, etc), and min-maxing and/or crafting obsessed protagonists.  

The Chaos Seeds

In the Chaos Seeds, a dark force plotting on a Jupiter-sized world called the Land decides to summon humans from Earth using a video game, whereupon he believes the Chaotic nature of the humans of Earth (who all have a bit of Chaos in their souls) will destroy the seals holding his kind.  Richter, the protagonist, is one of the first such individuals.  Richter is a clever man who was also a heavy gamer on Earth, and his reaction to be ripped from his homeworld is oddly muted (at first).  Rather, he quickly throws himself into adapting to his new world, making the best of it, mostly forgetting Earth as irrelevant.  This story has a lot of fighting, crafting, and town-building for those interested in those things.  I will also say that it doesn't make one of the greater mistakes some litrpgs make, such as making brain-shots non-fatal if the individual has high hp, lol.

Singularity Online

To be honest, this is one of my favorites (a relatively recent one).  Essentially, the protagonist, a guy named Jeff from a future that seems just one step removed from the horrors of Giga's Baldr series, is a programmer involved with the company making a VRMMO named Singularity Online.  The setting of the game is an interesting combo of Lord of the Rings and Wheel of Time setups, with corrupted races, a powerful and unkillable ultimate evil, and enclaves of the Light surrounded by Blight and Darkness.  Jeff, who is a genius programmer and scientist, through the game's system, manages to gain the class of Sorcerer, which allows him to make his own spells (yes, very D&D), though this requires imagination, inspiration, will, and passion to succeed.  Jeff is a pretty all-around awesome guy, in that he has a powerful sense of self, a strong sense of compassion, and a knack for figuring out stuff he wasn't supposed to.  Reading his story as he works is one of the better litrpg experiences out there, at least so far.

The Silver Fox and Western Hero

I'll be honest.  This is actually more Wuxia than litrpg, with the only litrpg element being the protagonist's ability to look at his progression in cultivation.  The protagonist of this story suffers from racism constantly throughout the story, with only rare individuals considering him on a personal level instead of a racial level.  Not only this, he is constantly forced to weather assaults from all fronts in his path toward ascendance, with allies suffering for getting involved with him and those he loves constantly under the most horrific of threats.  He is an insanely stubborn individual, determined to find his own path, forever denying the easy way.  While this series can be immensely stressful, it is also very good, so far.

Ten Realms

This series begins with the Two Week Curse, which is both the name of the first book and the name of a phenomena where people from Earth spontaneously begin displaying semi-magical abilities before suddenly disappearing two weeks later.  Erik and Rugrat are mercenaries, playing bodyguard to people from a parasite corporation in a war-torn African nation (unnamed), until they get ambushed (due to their client being a total moron) and Erik loses his legs and gets the Two Week Curse.  They immediately begin to prepare, with Erik using his newfound mana to create a healing spell that lets him regrow his legs and Rugrat building a capsule full of guns and supplies to take with them.  They are then taken to the new world, the Ten Realms, a game-like world with a mix of traditional leveling and cultivation.  Most of the series, so far, has Erik and Rugrat forging a path of progression while dragging their increasing (rapidly) number of followers in their wake.  Erik is the one who constantly pushes the limits of what is possible, while Rugrat tends to rest a little more on his natural talent than his friend, while also supporting him in various ways.  One of the most important things of this series is the soldiers' bond between Erik and Rugrat, that of two men who trust each other utterly, knowing both their own abilities and those of their partner.  It adds a rather unusual flavor to the usual litrpg/Wuxia combo.

Conclusion

These are the series that have left the best impression on me over the last three months.  While I've read almost forty series and ninety books, these are the ones that stood out the most.