Great thread idea. I'm only going to particularly do series though because I don't think I'll ever be able to nail down my top ten favorite games. I though Smash Ultimate was going to finally be my number one of all-time but I'm not quite comfortable saying that even with how much I love it. Also going to throw a little flavour into here, making sure to throw out my favorite games in the series as well as my least, and maybe a quick comment. I hope it's quick. Also, rough order only.
I. Super Smash Bros. Series
Series Highlight ~ Smash Bros. Ultimate
Series low-point ~ Super Smash Bros. [64]
Super Smash Bros. has evolved from a cool little collection of Nintendo all-stars into an all-out celebration of video game history (granted, with a heavy Nintendo focus but when both Cloud Strife and Shovel Knight are in your game, it truly feels bigger than Nintendo). The amount of love and passion poured into these games, Ultimate especially, is staggering. And as an aside, it's crossover nature makes it the best game to follow news for prior to it's release. Smash Directs last year were big events, and pretty much the only thing to get me genuinely excited. Glad the DLC keeps it coming, the Joker reveal was amazing. Only real downside about this as a series is, more than most other games on this list, I feel each iteration kinda invalidates the earlier ones. I can have fun with any of them, but I have less desire to return to any of them when Ultimate exists.
II. Sonic The Hedgehog
Series Highlights ~ Sonic Generations & Sonic Mania
Series Low-point ~ Sonic the Hedgehog 06
After Dragon Ball Z, Sonic is the property I most associated with my childhood, and I've played Sonic the Hedgehog 2 more times than I can count, as well I've bought it more times than I dare to count. Sonic Adventure 2 Battle is also a game that dominated my life for quite some time. And while Sonic certainly had plenty of awful titles, ultimately to me it'll always be a proud piece of nostalgia, as the series consistently provides amazing soundtracks and the speed based platforming provides a thrill, a sense of bad-assery, that most other platformers just don't replicate.
III. Donkey Kong Country
Series Highlight ~ Donkey Kong Country
Series Low-point ~ Returns. Unless you count 64, which I don't.
Make no mistake about it, Sonic's positioned above it mostly due to stronger emotional connection, because the Donkey Kong Country series are, bar none, the best platformers out there. At least, for side-scrolling platformers. Donkey Kong Country is my favorite of the four, mostly because I feel it's the only one to strike the perfect balance of difficulty and fun (The Squawk levels come to mind from 2, 3 was straight up unfair at points, & Tropical Freeze kinda nails this actually, but it added a breathing meter to the underwater levels so it's not my favorite on principle alone) but I'd put all three and Tropical Freeze above most other platformers from any series. Fantastic aesthetics, gameplay, music (DKC 2 especially). Honestly, probably pound-for-pound the strongest series on this list. I hacked my SNES Classic entirely because I wanted to play these games again.
IV. Danganronpa
Series Highlight ~ Super Danganronpa 2: Goodbye Despair
Series Low-point ~ Danganronpa Another Episode: Ultra Despair Girls
The only visual novel series I've played and damn, what a fantastic ride that was. I have a lot of admiration and respect for what Kodaka did with this series (both the games, and the highly ambitious anime send-off). The high absurdity cartoon antics combined with the dense highly thematic through line and strong emotional sincerity is a mixture I absolutely adore, and in it's perfected form, Danganronpa 2, it lead to my favorite story I've experienced in a video game. The ending of that game is one of my favorite endings in any medium. There's not much reason to revisit the games though once completing and in a sense, I only truly love Danganronpa 2 out of the series, but that doesn't mean I don't hold affection or admiration for the other entries (V3 was also highly ambitious, and did a lot with the narrative to increase player involvement in a way that was really fascinating to me).
V. Tony Hawk's Pro Skater & Underground
Series Highlight ~ Tony Hawk's Pro Skater 3
Series Low-point ~ Tony Hawk's Pro Skater HD
I haven't played any of the other Tony Hawk games outside of the Pro Skater & THUG entries, I'm sure there's worse in the others. Anyway, Tony Hawk is probably the quintessential pick-up & play immediate fun game series there was. The 2:00 limit seemed specifically designed with that model in mind, and I've spent countless hours in those games and it was always a joy. THPS3 feels like one of those rare perfect games, like it accomplishes everything it tried to do expertly. THUG's storyline was actually pretty solid, and Eric Sparrow is one of the most easily hateable villains out there. While THUG2's story was way worse, that's actually my second favorite of the series. And I should throw this out, it's absolutely appalling that THPS5 was released in a state where they needed a patch bigger than the game itself to fix it but honestly, I had a lot of fun with THPS5 post-patch, the online functionality meaning it's unplayable now is pretty upsetting to me.
VI. Kirby
Series Highlight ~ Planet Robobot
Series Low-point ~ Dream Course
There's a good sense of nostalgia here too, with Kirby Super Star Saga being second only to Sonic 2 for the most played games of my youth. Even to the point where a certain boss' appearance in Ultimate, had me jumping out of my seat repressing those tears of joy. Regardless, what the Kirby games lack in challenge, they more than make up for it in personality, cuteness, great boss fights with demonic beings, and catchy/pleasant music. They have stuck with the current formula a tad too long, and Star Allies was seriously close to being the low-point if it wasn't for the fanservice DLC characters and the legitimately fantastic final boss, so I hope the new one is something new but it's still always a fun time. And Air Ride's City Trial mode is always a blast.
VII. Xenosaga
Series Highlight ~ Episode I: Der Wille zur Macht
Series Low-point ~ Episode II: Jenseits von Gut und Böse
Episode I is actually the only game in the series I've beaten, though I stopped at the final boss of Episode III I believed. Still, that doesn't stop the amount of affection I have for Episode I, and trust me, I loved Episode III too (thankfully, Episode III was designed to be friendly to those who skipped Episode II) and really enjoyed how the second half was structured, with a series of these big boss battle pay-offs one after another. And though my time with Episode II was comparatively short, it has one of the best battle systems in an RPG, though admittedly it's never very well-utilized from my understanding (I find it disappointing that Episode III opted for a very generic battle system instead of improving the one from II or returning back to the one from I [which I'm also, extremely fond of] [in fairness to Episode III, in II everyone shared the same skill tree, which I hated]). The story, the unholy amount of time dedicated to cutscenes, the characters, the pacing, I loved pretty much it all. Episode I is my favorite RPG, granted, I haven't had the time to sink into most RPGs since a lot of them insist on being forever hours long but still, I'm grateful that Xenosaga came to me at a time where I had those hours to sink.
VIII. Mario Kart
Series Highlight ~ DS or 8 Deluxe (8 Deluxe would win this if it had a Mission mode)
Series Low-point ~ Super Circuit
Much like TH, this falls under the quick, pick-up and play fun. All entries, well most entries, are really fun and I love how this series utilizes it's wide history. Having an equal amount of new and retro tracks is probably the best feature of the series, and it's baffling to me that Mario's other big spin-off series, Mario Party, hasn't yet incorporated that model (Super Mario Party would've been a lot better had they had some retro maps thrown in, even if it was just one or two more). Not much to say here, except I need to buy 7 at some point cause it's the only one I've never touched.
IX. Soul Calibur
Series Highlight ~ Soul Calibur III
Series Low-point ~ Soul Calibur Lost Swords
When it comes to fighting games, if we're not counting Smash, Soul Calibur is my field of choice. I wasn't exposed to Tekken until much later, only really getting to play two of the games (though they're very fun too) but I love Soul Calibur's gameplay as opposed to the traditional fighters. The buttons corresponding to vertical & horizontal attacks are a lot easier for me to register, and having a block button was something that felt more natural to a younger me than holding back (I'm cool with that now). I love the guest fighters (only got into this series for Link), and several of the special modes specific to each game (I'd kill for another Chronicles of Sword type mode though).
X. Super Mario
Series Highlight ~ Super Mario Odyssey
Series Low-point ~ New Super Mario Bros. Wii
To be honest, this is mostly for the 3D entries, I'm not huge on most of Mario's side-scrolling catalogue (though World & Bros 3 are great). It's not that they're bad, they're all fun but they kinda like the special spark that 64, Sunshine, or Odyssey has. Presumably Galaxy too, never got around to that one. Mario can be pretty basic in terms of flavour, and I feel there's more individual personalities in many other platformer series, but ultimately, when it comes to gaming fundamentals, Mario has it nailed. And every now and again, Mario will deliver something like Odyssey, and that's enough to keep him up here.
