I usually watch a lot of older anime mainly so I've heard and seen my fair share of anime that have surprised me with the quality that aren't talked about often and especially within some of those parts.
First anime - Infinite Ryvius:
I watched it cause of the premise I read up about it at first, a cross between Lost in Space and Lord of the Flies (I love Lord of the Flies a ton). The description isn't too far off the idea but what surprised me is how it plays off the idea when you have a lot of young people (at most oldest being at least young adults) as the ship is lead by teenagers trying to maintain order but only getting more chaotic as stuff gets leaked behind the scenes, people getting tired of living on a ship, etc. Eventually breaking to a boiling point. Great psychological stuff overall, would recommend if anyone enjoys slow works which was unexpected by the director Goro Taniguchi who is normally not this slow from what I seen of his works (Code Geass and Gun X Sword).
Second anime - Gear Fighter Dendoh:
Another mecha series that deserves more love, I heard of it mainly due to playing SRW MX at the time and seeing this series in the game that looked fun. Decided to watch it during my walkthrough and it was a lot better than I expected. It follows the MOTW format as it's main thing is that it focuses on two pilots, Hokuto and Ginga who are kinda opposites in personalities but have the right idea when it comes to piloting the main mecha Dendoh. Aliens invade Earth and they happen to accidentally find this mecha and now as the pilots, they have to defend the planet as they deal with school life. I found it endearing as it's also a love letter to the 70s mecha as it references Raideen, Combattler V, and Mazinger Z. They even reference their trademark weapons! It's not the most complicated series out there but it's a great MOTW if you enjoy that kind of goodness.
Third Anime - Nadia: The Secret of Blue Water:
This is my favorite anime from Hideaki Anno, Nadia is a series that deserves a ton of love as it's the one work that doesn't get talked about often (it's either Evangelion or GunBuster when it comes to Anno). It's really more of a adventure anime if anything with a plot that slowly gets revealed as the series goes on, as there's an antagonist who happens to have a machine that is a threat and a small crew riding in a advance ship to fight back against his plan but the main characters with the series are just thrown along the wave with whatever happens that happens to include that main plot. Eventually the plot then focus on that part but a lot of the time the main characters in general are just put in many situations. Would recommend overall if you like the adventure kind of anime or if you want to see the work that put Gainax into the situation that led to the creation of Evangelion.
Honorable mentions:
Hades Project Zeorymer:
Sick OVA series that has my favorite super robot design of all time and great animation, a pretty basic but good story for it's length but it's a great time if you wanna see a super robot that's actually OP fight against other insane mechas (and being broken in any of the SRWs it's in).
Magic Knight Rayearth:
It's magical girl and mecha combined that's drawn by CLAMP, must I say more?
Super Heavy God Gravion:
Another MOTW from the early 2000s, it's spilt in two halves, from Gravion to Gravion Zwei. Honestly it's not another deep series but it does a good job at telling some surprising good stuff given it's a Obari series (.t the horny animator who also does mecha). Good series overall and do recommend if you want a MOTW mecha series with some killer music from Jam Project, cool mecha action and a pretty good plot. Oh and having the best mecha combination theme I have heard still to this day.
