Alright, I'm mostly a RPG or Adventure man, and I seldom play arcades/platformers. However, I did enjoy them in the past, and they're a good way to break the monotony of the RPG/Adventure mechanics, as well as to satisfy that twitchy itch. Many years ago, I enjoyed Commander Keen 4-6 and Captain Claw for their cartoonish graphics and excellent gameplay. The latter especially because it had different ways of dealing with enemies. On the other hand, I found Jazz Jackrabbit to be a bit bland. However, I like it best when the platforming gameplay is combined with some sort of character progression, be it in the form of skills, equipment or other things. That's why I also liked Zeliard – if anyone remembers, it was sort of a proto-Diablo game; a platformer with towns where you could trade equipment, purchase spells, store money etc., while the dungeons had some puzzle elements.

Can anyone suggest any similar game? Here on GOG or Steam, with at least some of the elements I listed above. But without all the frustrating elements that many platformers seem to suffer from, like the inability to save whenever you want (or checkpoints being spread too far apart), extremely tough levels, boring labyrinths and too much jumping.

This is a question, so the most convincing short description of a game will earn its poster 5 rep points, and I'll probably get that game.

I hate platformers. Therefore, it take very good ones for me to enjoy them. But on the other hand, maybe it takes platformars that aren't platformers.

For instance : Unepic. Is that a platformer ?

And Prince of Persia, the original one. That's quite the platformer, isn't it.

I wonder if Bullfrog's Flood is available somewhere. A platformer where you stick on the walls. Neat.

And have you tried Braid ?

Try "Mark of the Ninja"...

Rogue Legacy. Progression, random levels and everything.

The later POP is kind of platformy as well. It's designed to allow you to sweep, slide, climb and jump across an open world seemlessly. Also, it's very forgiving and any mishaps during your travels are non-fatal due to your rather foxy NPC who'll save you everytime.

It's therefore perfect if you just want a light-hearted platformer without the frustration.

Try the first Rayman or Abe’s Oddysee / Exoddus, or Earthworm Jim. All are very good games and as I am no platformer fan the fact I still enjoyed them stands out for me personally.

I also got you the link to all the games GOG list as platformers and I would suggest that you also give Psychonauts some consideration.
http://www.gog.com/catalogue?search=platformer

Of the recommended games, I've played Prince of Persia, Hocus Pocus, Earthworm Jim and Abe's Odyssey. They were neat, but not what I'm looking for here. I'd like a platformer with a little bit of meat to it, not just jumping from one moving platform to another and collecting goodies in the air.

Castlevania actually sounds good as it seems to have a decent story/setting, but it's a console-exclusive title, no?

Spelunky - the game which just keeps on giving - http://spelunkyworld.com/original.html

Hmm, yes, I might try the freeware version if it's anything like the game to be released in a week. There's certainly a bit of hype being built around it.

The Swapper - http://facepalmgames.com/the-swapper/

Excellent sci-fi story with beautiful aesthetics, clever puzzles and a gorgeous Soundtrack! My Goty 2013 so far ;)

My default recommendation for PC platformers is Rayman Origins (and maybe Rayman Legends when that comes out). There isn't really any progression in terms of skills, but it definitely ticks the checkboxes for excellent gameplay and cartoonish graphics. And those graphics look absolutely gorgeous.

It is not a game even close to being finished yet, but if you are also looking for stunning pixel art and metroidvania, then Iconoclasts by Joakim Sandberg is definitely a game to look out for. You download a demo alpha level from last year here - http://www.konjak.org/?folder=4&file=30

Also - http://www.youtube.com/watch?v=VZE7kGax7Ds

Of the platformers here on GOG I would highly recommend Rogue Legacy, Earthworm Jim 1+2, The Rayman series (especially Rayman Forever and Rayman Origins, since Rayman 2 and 3 are 3D platformers, and I don't know how much are you into that), Oddworld: Abe's Oddysee and Abe's Exoddus (these are puzzle platformers, but still unsurpassed).

If you'd like a real mix of platformer and RPG/hack-and-slash, but with a greater focus on the RPG sides of it, please, give Nox a go. It starts out easy enough, with the first missions being really accessible, but it soon becomes more and more demanding, while never ceasing to feel rewarding. You can jump at will and push almost every object, which makes for some interesting puzzle design. Really, if you haven't played it already, go give Nox a try. Especially if you're a fan of RPGs in the Diablo style, Nox is your thing. Actually, Nox is your thing if you like action, platforming, dungeon crawling, puzzle solving, adventure... you name it. I guess only the strategy games fans wouldn't see the appeal, as it's quite an action-packed title from beginning to end, with the only cerebral "strategy" involved being the one you need to instinctively develop when tackling enemies or environmental puzzles.

Go buy Nox. Or any other platformer suggestion, so far they've been pretty solid. But Nox, as well. Pretty please?