The "Best" is definitely subject to opinion, as what I like may be the opposite of what you like!

There are two types of platformers in my mind -- Those that are totally addictive that you don't want to stop playing (you know, the ones where you want to find every single coin, crystal, banana, etc. and discover every secret and Easter egg,) and the "Eh~ It's OK," type of platformers that you only play when very bored. I'll give a few examples based upon console titles:

For me, addictive titles were the Donkey Kong Country games (#3 was my least favorite of the three), Super Mario Brothers, Donkey Kong 64, Banjo Tooie (probably the best 3D platform-adventure I've ever played!)

"Meh" titles: Super Mario Brothers 2, Sonic the Hedgehog, Super Mario 64 (it was OK, but I never have finished it.)

So, here are lists of the PC Platformers that I've tried (trying to keep my comments short, so I don't overwhelm you! ☺ ) :

Really enjoyed:

Giana Sisters games - Gorgeous artwork that changes instantly when you switch characters. The differing abilities of each really adds to the fun of puzzle-solving.
Nihilumbra - Beautiful, compelling story, which takes ~ 2 hours to complete. Devilishly hard puzzles afterwards!
Trine 2 - Gorgeous artwork, fun puzzles; not a lot of emphasis on fighting (Have #1, haven't tried, yet)
I started Treasure Adventure Game, and it actually looks like one I'll enjoy! Reminds me of my old C64 days! lol~

Braid is very good, but it was just too devilishly hard for me.

Didn't really enjoy:

Castle of Illusion - Very Super Mario 64 in feeling. It's OK, but nothing that really draws the interest.
Knytt Underground - beautiful background art, but lame dialogue and no addictiveness -- at least not in the short time that I played.

Games I'm interested in trying:

Brothers: A Tale of Two Sons (I know it's an adventure, but it has platformer elements I think -- Own but not played)
The Cave (own, have not played)
Contrast *****(please VOTE to bring it to GOG!) *****
Dust: An Elysian Tail (Own, not played)
Guacamelee! Gold Edition (Own, not played)
Knock-knock
Lucidity
Prince of Persia: The Sands of Time
Psychonauts (Own, not played)
Rayman 2: The Great Escape (I hear this one is like DK64 and Banjo Tooie?)
Stick it to the Man!
Violett

Wow... my list of tried PC platformers is way shorter than I thought it would be! :o

Based upon my lists, are there any on my Games-of-interest list that I should avoid or move to the top of my wishlist? Any games you can recommend that are not listed? What are your favorites and least favorites?

Good list, got some of those, will nosey at those I don`t.

Some suggestions:

PID - http://www.gog.com/game/pid
Excellent platformer with great graphics/audio.

Spelunky - http://www.gog.com/game/spelunky
Addictive platformer, has kept me hooked for far too long.

P.S. Original Trine is well worth a shot too.

Thank you, fishbaits ^__^ I've added both to my wishlist to remind me to check them out!

I just finished Dust and Guacamelee. Both are good, although Guacamelee really sucked me in right away with its style and good controls, whereas Dust's combat is a little too basic and it's heavy on the cutscenes for my tastes.

Psychonauts is one of my favorite games from the past decade or so. I've beaten it multiple times and I'm sure I'll play it again in the not too distant future.
Prince of Persia: Sands of Time is very good.

I second the Spelunky recommendation. I loved the freeware version and the remake is even better.

I loved UnEpic but the protagonist may not be for everyone.

Thanks for the feedback! I've got Psychonauts installed on my computer, but I need to wait 'til I get a PC-compatible controller before I play it, I think.

Every time someone mentions Spelunky, I'm thinking of the old C64 game, Spelunker, which I used to play over and over again when I was young!

Pid Steam keys were free for a time.

If you like Mario, you should give Eversion a try. It's Mario meets Silent Hill. :P
If you like cutesy games, then Toki Tori is also great. And if you haven't played it, LIMBO is a good one time play. Which reminds me, you didn't mention Super Meat Boy. That game is cray cray.

There's not too much like the Banjo/Spyro/etc. platformers out there on PC. Maybe a Pacman World title? But they're making Crash Bandicoot HD for PC and I'm pretty excited for that. You might also want to look into Papo & Yo for 3d platformers.

UnEpic is actually one I've been watching for a while, just wasn't sure it was for me. I prefer puzzles to fighting, but then, it really depends on the game!

By the way, I'm up-repping all of the feedback, 'cause I just appreciate it so much :D

I recently completed both Guacamelee and Dust and they are both good. Very good. Each is bit different, Guacamelee with very unusual but nice world and visuals and with fantastic combat. Dust has more simple combat, but more interesting story and characters and looks gorgeous.

What is missing on your list are new Rayman games. Rayman Origins and Legends. Those are fantastic, in my opinion better than old Raymans, and if you have someone to play them with then they are probably the best platformers available.

You should try the swapper. It has a great storyline and some pretty good puzzles. The story was phenomenal.

LIMBO, Papa & Yo, and Eversion added to my wishlist. I'm kicking myself because Papa & Yo was on special recently, and I didn't get it! >_<

Spyro is console-related, I'm guessing?

I thought I had that! but I guess not! Adding to the list!

I love platformers, but I'm more into the exploration-driven stuff like Rareware's N64 games, Jak & Daxter, Castlevania: Symphony of the Night, and other "collect-a-thons" and "Metroidvanias". This is why I'm really looking forward to A Hat in Time, and plan to play Dust and Guacamelee when I have a better computer (own them, but they run like crap on my old laptop).

I personally highly recommend Psychonauts, mainly for the humor and sheer imaginative variety in the levels. It's completely unforgettable from start to finish, and one of my favorite games ever.

Rayman 2 is actually pretty different from Rareware's stuff, despite coming from the same era. It's a bit more linear, and has a much larger focus on straightforward platforming and a little bit of combat rather than exploration and collecting stuff, but there are secrets to be found if you want to go off the beaten path. It's pretty good though mainly due to doing it's own thing and not following the crowd and just doing what Mario 64 did. Rayman Origins and Legends were fantastic too. They're side-scrollers and more linear than Rayman 2, but the absolutely superb controls and excellent level design makes it a joy to play.

I also think Sands of Time would be up your alley based on how you enjoyed the puzzle-solving elements of various other platformers. The actual platforming is a but unconventional, but super fun and flows really well. Haven't played the sequels, so I can't speak for them.

Also I recommend Spelunky too, alongside several other users in this thread, it seems!

Wonderful information in your post, thank you so much! I'm with you on the exploration driven stuff, hence my love DK64 and Banjo Tooie! What is Jak and Daxter? A console game? I looked at Castlevania: Symphony of the Night recently, and it looked like an RPG? Should I be adding that to my list?

I've seen the "Metroidvanias" description before, but I don't know what it means *^_^* What is it about Metroid (never played) that is so unique?

You definitely gotta play Psychonauts

Jak & Daxter is a trilogy on the PS2. The first one started out as a 3D platformer very reminiscent of the classic N64 platformers with lots of collecting and exploring, set in a fairly unique world. It was followed by two games, Jak 2 and Jak 3, which took the series in a bit of a different direction, taking elements from GTA of all things by giving you an open world to do missions in, the ability to drive vehicles and some guns to use in combat. The first Jak & Daxter remains my personal favorite, but Jak 2 and 3 are still pretty good and many consider them to be the better games in the series.

As for a definition of Metroidvania, it's mainly used to refer to non-linear 2D platformers. They're often characterized by exploring large non-linear worlds in which you find upgrades and power-ups which allow you to explore even further by opening up more areas of the world. For example, in Metroid there are several areas that will be blocked off by rocks, but once you find an upgrade that lets you drop bombs you can blow up the rocks and continue in that direction.

Symphony of the Night has RPG elements, but it's certainly a platformer first and foremost. You level up and can change your equipment, but the main focus is the running and jumping, exploring and fighting monsters throughout Dracula's massive castle, while gaining new abilities that help you explore further. The Castlevania games on the DS and GBA are done in a similar style to Symphony of the Night too.